EPA

DRAFT, FEBRUARY 1987

IMPROVING ACCURACY AND REDUCING COSTS OF

ENVIRONMENTAL BENEFIT ASSESSMENTS

Reconciling Averting Behavior and Contingent

Valuation Benefit Estimates of

Reducing Symptoms of Ozone Exposure

by

Mark Dickie

Shelby Gerking

David Brookshire

Don Coursey

William Schulze

Anne Coulson

Donald Tashkin

USEPA COOPERATIVE AGREEMENT #CR812054-01-2

Project Officer

Dr. Alan Carlin

Office of Policy, Planning and Evaluation

U.S. Environmental Protection Agency

Washington, D.C. 20460

OFFICE OF POLICY, PLANNING AND EVALUATION

U.S. ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460
CONTENTS 

Tables ................................ 

iii 

1. Introduction ........................ 1 

2. Policy Context and Literature Review ............ 3 

3. Data ............................ 13 

4. Results ........................... 14 

5. Summary and Conclusions ................... 36 

References .............................. 38 

Appendices 

A. Revised Follow-Up Questionnaire ............... 41 
TABLES 

Number Page 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

Averting Behavior and WTP: Normal Subsample . . . . . . . . . . 

Averting Behavior and WTP: Impaired Subsample . . . . . . . . . 

CVM Estimates of WTP for Avoiding Symptoms for One Day . . . . . 

Mean and Median WTP to Avoid Symptoms . . . . . . . . . . . . . 

Daily WTP to Avoid Symptoms . . . . . . . . . . . . . . . . . . 

Frequency Distribution for Contingent Valuation Bids to 

Eliminate Up to Three Most Bothersome Symptoms for a Month . . 

Summary of CVM Bids to Avoid Sinus Pain or Discomfort For 

One Day . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Summary of CVM Bids to Avoid Cough For One Day . . . . . . . . . 

Summary of CVM Bids to Avoid Throat Irritation For One Day . . . 

Summary of CVM Bids to Avoid Chest Tight For One Day . . . . . . 

Summary of CVM Bids to Avoid Could Not Breathe Deep 

For One Day . . . . . . . . . . . . . . . . . . . . . . . . . 

Summary of CVM Bids to Avoid Pain on Deep Breath For One Day . . 

Summary of CVM Bids to Avoid Out of Breath Easily For One Day . 

Summary of CVM Bids to Avoid Wheezing/Whistling Breath 

For One Day . . . . . . . . . . . . . . . . . . . . . . . . . 

Summary of CVM Bids to Avoid Headache For One Day . . . . . . . 

Cross Tabulation of Mitigation by Bid . . . . . . . . . . . . . 

Cross Tabulation of Mitigation by Symptom Severity . . . . . . . 

Means of Contingent Valuation Method Bids to Avoid Symptoms 

for Normal and Respiratory Impaired Respondents . . . . . . . 

Regression Results: Revised Contingent Valuation Bids Used As 

Dependent Variables . . . . . . . . . . . . . . . . . . . . . 

5 

6 

8 

10 

12 

15 

17 

18 

19 

20 

21 

22 

23 

24 

25 

29 

30 

32 

33 
Notice

This document is a preliminary draft. It has not been formally

released by the U.S. Environmental Protection Agency and should

not at this stage be construed to represent Agency policy. It is

being circulated for comments on its technical merit and policy

implications.

1. INTRODUCTION

Previous applications of the contingent valuation method (CVM) have

resulted in comparatively large estimates of willingness to pay (WTP) to

avoid symptoms of ozone exposure. Berger et al. (1985), for example,

found that raw averages of CVM bids to avoid one day of cough and

headache were $105 and $173, respectively. Moreover, Dickie et al.

(1986) reported that averages of CVM bids to avoid these and other ozone

symptoms such as chest tightness, throat irritation, and pain on deep

inhalation always were larger than corresponding estimates obtained using

the averting behavior method (ABM). Frequently, average CVM bids

exceeded their ABM counterparts by factors between five and ten. A

number of conjectures were advanced to explain this discrepancy; but none

could be firmly supported. As a consequence, policy makers interested in

establishing dollar benefits of reduced ozone symptoms are forced to

choose between two sets of highly divergent estimates of WTP.

This report uses a new data set to reconcile differences between CVM

and ABM estimates of reduced ozone-related health symptoms. The

reconciliation approach, which focuses on the CVM, involves three steps.

First, each respondent is directly asked for his WTP to avoid one day of

recently experienced ozone-related symptoms such as headache, cough, and

chest tightness. Second, each bid is multiplied by the number of times
per month that a symptom occurs and monthly bids are totaled across

symptoms. Third, respondents are advised of these totals and given an

opportunity to revise their bids. Results obtained from new data collected

during July-October, 1986 from 221 residents of Glendora and Burbank,

California reveal that averages of revised bids are dramatically lower than

averages of original bids. For example, original bids to avoid one day of

cough averaged $355.10, whereas revised bids averaged $1.24; original bids

to avoid one day of headache averaged $178.39, whereas revised bids

averaged $1.19. These results suggest that in CVM studies of frequently

occurring events such as health symptoms, care should be taken to ensure

that respondents are aware of the implications of their bids for total

expenditure. Moreover, revised bids to eliminate one day of all nine ozone

symptoms considered actually are lower than corresponding ABM estimates.

This relationship between the two sets of estimates should be expected, as

explained more fully in Dickie et al., because ABM overestimates WTP. In

addition to reducing symptoms, averting goods used in the ABM calculations

may represent sources of direct utility.

The remainder of this report, which is submitted as part of a larger

on-going study of morbidity-ozone relationships, is divided into four

sections. Section 2 briefly reviews previous estimates of WTP to reduce

minor symptomatic discomforts and stresses reasons why such estimates are

important in a policy context. Section 3 highlights key features of data

used to implement the three step approach to obtaining revised CVM bids.

Section 4 presents the original and revised CVM estimates of WTP to avoid

ozone related symptoms. Also presented in Section 4 are supplementary

2
tabulations and regression results that explain the behavior of individual

CVM bids. A summary and conclusions are presented in Section 5.

2 . POLICY CONTEXT AND LITERATURE REVIEW

Reducing symptoms or discomforts of ozone exposure is an important

source of dollar benefits for three interrelated reasons. First, as

discussed more fully in Gerking et al. (1984), minor symptomatic

discomforts can occur even in healthy adults at ambient ozone levels below

the present federal standard of 12 pphm. Second, even though these

discomforts are less serious than diseases such as asthma, emphysema, and

chronic bronchitis, they do cause individuals to limit activities. Third,

these discomforts and activity limitations are experienced by a large share

of the exposed population. As a consequence, willingness to pay to avoid

them may be substantial and should be taken into account in the regulatory

impact assessment process.

Three methods have been used to measure benefits of reduced health

symptoms of ozone exposure: (1) cost of illness (COI), (2) averting

behavior (ABM), and (3) contingent valuation (CVM). Unfortunately, these

methods have produced widely divergent benefit estimates. This point is

documented in the remainder of this section through a brief survey of

pertinent literature. Readers interested in a more complete and evaluative

review are referred to Chestnut and Violette (1984) and Dickie et al.

(1986). Application of COI tends to result in small benefit estimates

because it considers only direct and indirect expenditures required for

symptom relief. Examples of costs considered by this method include

medical expenses and income foregone due to work loss. A fundamental

criticism of the cost of illness approach, however, is that willingness to

3
pay (WTP) to avoid symptoms is not correctly measured. Harrington and

Portney (1987) and Berger et al. (1985) argue that on theoretical grounds,

WTP generally exceeds COI estimates because the latter accounts neither for

the disutility effects of symptoms (i.e., "pain and suffering") nor for

defensive expenditures for goods other than medical care. Empirical

studies confirm this finding. Rowe and Chestnut (1986) estimate the ratio

of WTP/COI for reduced bad asthma days to be approximately 2.0. Benefit

calculations for 10 percent reductions in ambient ozone levels by Dickie

(1987) yield corresponding ratios of approximately 5 for normal individuals

and 11 for individuals with respiratory impairments. Consequently, the

CVM, in which individuals are asked directly for their WTP to avoid

symptoms, and the ABM, in which WTP is inferred from individual behavior,

have received increasing attention.

There also are substantial differences between estimates of WTP using

the ABM and CVM approaches. Although there have been several theoretical

studies relating to the ABM (i.e., Harrington and Portney, 1987; Berger et

al., 1985; Courant and Porter, 1981; Harford, 1984; Bockstael and

McConnell, 1983; and Bartik, 1986), Gerking and Stanley (1986) and Dickie

et al. (1986) represent the only attempts to apply this approach in an

empirical setting. Gerking and Stanley estimate benefits of ozone control

in St. Louis and Dickie et al. estimate benefits of reduced ozone-related

minor symptomatic discomforts. In the latter study, calculations of WTP

were obtained by combining estimates of the marginal product of averting

activities in reducing symptoms with direct data on the costs of those

averting activities. These calculations, shown in Tables 1 and 2, pertain

to persons with normal respiratory function and those with impaired

4
TABLE 1. AVERTING BEHAVIOR AND WTP: NORMAL SUBSAMPLE

Symptom

Could Not

Breathe Deep

Pain on Deep

Inhalation

Change in

Averting

Expected

Probability

WTP per

Good

Symptom-Days

of Symptom

Symptom-Day

Avoided Avoided

--- a --- a --- a a ---

GASCOOK* .0079 2.88 $29.12

Out of Breath

Easily ---a --- a --- a --- a

Wheezing/

Whistling Breath --- a --- a a a --- ---

Chest Tight ACCAR*** .0116 4.25 $35.76

Cough ACCAR***

GASCOOK***

.0287 10.47 $14.18

.0866 31.63 $2.66

Throat

Irritation ACCAR*** .0291 10.63 $14.30

Sinus Pain ACCAR*** .0300 10.94 $13.89

Headache ACCAR* .0211 7.69 $19.77

a No coefficients of averting goods were correctly signed and statistically significant at

10 percent using a one-tail test in symptom production function.

*Denotes coefficient significant at .01 (one-tail) in symptom production function.

** Denotes coefficient significant at .05 (one-tail) in symptom production function.

***

Denotes coefficient significant at .10 (one-tail) in symptom production function.

SOURCE: Dickie et al. (1986, p. 6)

5
TABLE 2. AVERTING BEHAVIOR AND WTP: IMPAIRED SUBSAMPLE

Symptom

Could Not

Breathe Deep

Pain on Deep

inhalation

Out of Breath

Easily

Wheezing/

Whistling Breath

Chest Tight

Cough

Averting

Good

GASCOOK* *

ACCAR*

GASCOOK***

GASCOOK * *

*** ACHOME

ACHOME *

ACCAR *

GASCOOK ***

ACCAR*

Change in Expected

Probability Symptom-Days

of Symptom Avoided

.0908 33.14

.0258 9.41

.0954 34.82

.0781 28.51

.0677 24.70

.0476 17.38

.0709 25.88

.2376 86.71

.0536 19.56

WTP per

Symptom-Day

Avoided

$2.53

$16.15

$2.41

$2.94

$16.80

$23.87

$5.87

$0.97

$7.77

Throat

Irritation ACCAR ** .0685 24.99 $6.08

Sinus Pain ACHOME * * .0505 18.45 $22.49

Headache ACHOME*

.0629 22.96 $18.07

APHOME*

.0634 23.41 $5.21

* Denotes coefficient significant at .01 (one-tail) in symptom production function.

* *Denotes coefficient significant at .05 (one-tail) in symptom production function.

***Denotes coefficient significant at .10 (one-tail) in symptom production function.

SOURCE: Dickie et al. (1986, p. 7)

6
respiratory function. In these tables, the first column on the left hand

side lists symptoms of ozone exposure and the second column lists the

averting activity (or activities) used in the marginal product and price

calculations. As shown, the four averting activities used are: (1)

automobile air conditioning (ACCAR), (2) home air conditioning (ACHOME),

(3) home air purifier (APHOME), and (4) switching from gas to electric

cooking (GASCOOK). The third column from the left gives the change in

daily probability of symptom occurrence as the averting good is employed;

and in the fourth column, the daily probability change is multiplied by 365

to obtain the expected number of days per year the symptom would be

avoided. Dividing the expected number of symptom days avoided into

annualized full prices for the averting good yields the WTP per symptom-day

avoided. Dickie et al. discuss these estimates more fully in Chapters 1

and 7 of their report; yet it is worth repeating that the four averting

goods analyzed may provide direct utility. Thus, the calculations of WTP

to avoid symptoms shown in Tables 1 and 2 are upper bound estimates. In

any case, Table 1 shows that WTP estimates for the normal subsample range

from $2.66 to avoid one day of cough to $35.76 to avoid one day of chest

tightness and four WTP estimates cluster in the range from $13.89 to

$19.77. WTP was not calculated for three symptoms, could not breathe deep,

out of breath easily, and wheezing/whistling breath, because respondents in

the normal subsample seldom experienced them. Table 2 shows that WTP

calculations for the respiratory impaired subsample for each of nine

symptoms considered range from $0.97 to $23.87.

Raw or unrevised CVM estimates of WTP to avoid one day of these

symptoms tend to be larger than those obtained by the ABM. Averages of CVM

7
TABLE 3. CVM ESTIMATES OF WTP FOR AVOIDING SYMPTOMS FOR ONE DAY

Symptom

Normal Impaired

Mean Bid Mean Bid

Could not Breathe Deep

Pain on Deep Inhalation

Out of Breath Easily

Wheezing/Whistling Breath

Chest Tight

Cough

Throat Irritation

Sinus Pain

Headache

$ 32

$ 42

$256

$ 12

$204

$140

$ 45

$ 97

$126

$271

$194

$374

$334

$198

$205

$213

$239

$154

SOURCE: Dickie et al. (1986, p. 15)

8
bids collected by Dickie et al. are reported in Table 3. These bids were

obtained from the same respondents who provided data to support the ABM WTP

estimates just discussed. CVM bids were obtained only from respondents who

reported having experienced the symptom within the previous 48 hours.

Consequently, bids are linked to specific, recent events that are fresh in

respondent's minds. As shown by comparing the figures in Table 3 with

those in Tables 1 and 2, the CVM bids for avoiding symptoms always are

larger than those obtained with the ABM, and certain CVM bids exceed their

ABM counterparts by a factor 10 or more. Also, in contrast to the ABM

estimates, the CVM bids from impaired individuals exceed those elicited

from normal individuals.

CVM bids obtained by Dickie et al. are roughly comparable to those

found by Loehman et al. (1979) and Berger et al. (1985), although the

latter studies did not distinguish between normal and respiratory impaired

respondents. The Loehman et al. study considered three classes of

symptoms: (1) shortness of breath/chest pain, (2) coughing/sneezing, and

(3) head congestion/eye, ear, or throat irritation. The three symptoms

were defined in terms of severity and duration as follows. A minor symptom

would allow continuation of normal daily activities, while a severe symptom

would require restriction of daily activities. Duration was defined as

one, seven, or 90 days. Approximately 1800 questionnaires were mailed to

residents of the Tampa Bay area of Florida; about 400 of these were

returned. Following an explanation that sometimes there exists a tradeoff

between discomfort and money, respondents were asked to value the symptoms

listed above by marking a payment card which listed 10 values ranging from

$0 to $1000. As shown in Table 4, mean CVM bids exceed the medians,

9
TABLE 4. MEAN AND MEDIAN WTP TO AVOID SYMPTOMS

(Loehman et al., 1979)

Days of Health Effect

1 7 90

Symptom Mean Median Mean Median Mean Median

Mild Shortness Breath $48.61 $ 4.90 $ 73.87 $13.64 $145.93 $35.96

Severe Shortness Breath 79.15 10.92 136.12 35.93 251.84 97.80

Mild Cough/Sneeze 26.40 2.31 44.67 7.84 86.03 22.85

Severe Cough/Sneeze 45.77 6.95 72.29 19.90 147.48 50.56

Mild Head Congestion/

Eye, Ear, Throat Irritation 32.50 3.80 41.51 9.58 90.37 25.14

Severe Head Congestion/

Eye, Ear, Throat Irritation 53.42 8.17 80.32 20.34 179.94 61.68

SOURCE: Dickie et al. (1986, p. 43)

10
reflecting a distribution skewed to the right. The authors suggest that

this skewness reflects extremely high bids from some respondents who may

have objected to the WTP question. As Chestnut and Violette (1984) point

out, however, the skewness may be partly attributable to the increasing

size of the increments between dollar amounts listed on the payment card as

the dollar amounts increased in size. Nevertheless, mean CVM bids shown in

Table 4 for eliminating symptoms for one day are higher than corresponding

ABM estimates for similarly defined symptoms. Also, after adjusting for

inflation between the late 1970s and the mid 1980s, the bids reported in

Table 4 are roughly comparable to those in Table 3.

The Berger et al. (1985) research considered seven symptoms: (1)

coughing spells, (2) stuffed up sinuses, (3) throat congestion, (4) itching

eyes, (5) drowsiness, (6) headache, and (7) nausea. Door-to-door and mall

intercept methods were used to sample 131 individuals in Denver and

Chicago; nine incomplete surveys reduced the number of observations to 122.

Respondents were asked the number of symptom days experienced in the

previous year and the costs associated with each symptom. Respondents then

were asked to rank the symptoms according to their relative undesirability

and to state their WTP for additional symptom-free days. Table 5 presents

mean CVM bids obtained in the Berger study. As was the case in Dickie et

al., only respondents who actually experienced the symptom were allowed to

bid. Mean bids obtained again are larger than those shown for similar

symptoms considered by Dickie et al. using the ABM method. Moreover, the

estimates imply that a hypothetical respondent experienced each of these

symptoms 10 days per year, he would be willing to pay nearly $8000 annually

to obtain complete relief.

11
TABLE 5. DAILY WTP TO AVOID SYMPTOMS

(Berger et al., 1985)

Symptom

Coughing Spells

Number

Experiencing

Symptoma

27

Mean

Daily WTP

$105.34

Stuffed Up Sinuses 43 38.84

Throat Congestion 24 43.93

Itching Eyes 16 172.23

Heavy Drowsiness 6 173.89

Headache 48 173.21

Nausea 18 91.24

aOnly those experiencing the symptom are included in calculating the

sample statistics.

SOURCE: Dickie et al. (1986, p. 46)

12
3. DATA

Data used to analyze CVM bids were collected by telephone interviews

of 221 residents of Glendora and Burbank, California. These individuals,

who previously participated in the UCLA study of Chronic Obstructive

Respiratory Disease (CORD) (Detels et al., 1979, 1981) were contacted

during the period July-October, 1986. Each of these individuals also

completed in-person baseline questionnaires and follow-up telephone

interviews that supported empirical work presented in Dickie et al.

Chapter 4 of that study discusses in greater detail characteristics of the

data and issues relating to sample selection.

An entirely new questionnaire was designed for the present study (see

Appendix A). The introductory section of this instrument updated

information on residence, employment, and earnings that previously was

collected in the Dickie et al. study. The next group of questions

ascertained which of 26 health symptoms the respondent experienced in the

past twelve months and asked the respondent to focus on those (up to three)

that were most bothersome. Then, more details were obtained about the most

bothersome symptoms. In particular, respondents were asked about the

frequency (both days in past month and days in past year), duration, and

severity of symptoms, as well as averting actions undertaken to make

themselves feel better. Information collected on averting activities

included: (1) specific actions taken to relieve symptoms, (2) change in

symptom severity brought about by these actions. Thus, the respondent was

led to think about his most bothersome symptoms as well as effectiveness of

averting actions prior to reporting WTP from a payment card in the

following contingent valuation question. This question was answered by

13
each respondent for up to three symptoms. If the respondent reported no

symptoms, WTP was not elicited. Finally, respondents were given an

opportunity to revise bids for symptom avoidance. Interviewers multiplied

the bids times frequency of occurrence during the previous month and then

added these values across symptoms. Total implied monthly expenditures to

avoid the most bothersome symptoms then were presented and respondents were

asked, "On a monthly basis, is [this total] what you would be willing to

pay to eliminate these symptoms?" If the response was negative, they were

first asked whether they instead would be willing to pay more or less and

then asked what dollar amount they instead would be willing to pay.

Of 221 respondents, 165 reported having at least one symptom, and thus

answered one or more contingent valuation questions. Data obtained from

raw or original bids implied the frequency distribution total monthly

expenditures to eliminate symptoms shown in Table 6. Values range from a

low of zero to a high of $899,910. The highest three implied monthly

expenditure figures are larger than annual income of any sample member.

Revised total monthly expenditure figures, shown in the second column of

Table 6, are much lower. These figures span zero to the $201-$300 range.

Confronting respondents with total monthly expenditure implications of

their original bids, therefore, results in dramatic revisions of amounts

that would be willingly spent to avoid symptoms.

4 . RESULTS

This section presents preliminary results of a further analysis of CVM

bids and related information that pertain to the nine ozone symptoms

considered by Dickie et al. (1986).

14
TABLE 6. FREQUENCY DISTRIBUTION FOR CONTINGENT VALUATION BIDS TO

ELIMINATE UP TO THREE MOST BOTHERSOME SYMPTOMS FOR A

MONTHa

Dollar Amount

Total Monthly Revised

Expenditure Implied Total Monthly

by Original Bids Expenditure

$ 0- 1

1- 10

11- 20

21- 30

31- 40

41- 50

51- 60

61- 70

71- 80

81- 90

91- 100

101- 150

151- 200

201- 300

301- 400

401- 500

501- 600

601- 700

701- 800

801- 900

901-1000

1001-1500

1501-2000

2001-3000

3001-4000

9,250

30,000

40,180

299,970

899,910

Missing

Observations

TOTAL 165 165

50 113

19 12

8 4

10 4

7 1

3 8

6 2

0 2

1 2

1 0

1 6

8 3

3 4

5 1

4 0

3 0

3 0

3 0

5 0

3 0

5 0

3 0

2 0

2 0

1 0

1 0

1 0

1 0

1 0

2 0

3 3

aFrequency distribution shows number of respondents.

15
Tables 7 through 15 provide frequency distributions and summary

statistics. Frequency distributions presented for each symptom show the

pattern of: (1) original or raw bids, (2) revised bids, and (3) revised

bids with exclusions based on consistency checks. For all except throat

irritation, out of breath easily, and wheezing/whistling breath,

distributions of original bids include at least one value of $9999 or more

(coded as $9999) to eliminate one day's experience with the symptom. For

the symptoms chest tight, pain on deep breath, and could not breathe deep,

at least one bid of $5000 also was reported. The next largest bids were

$500 to eliminate one day of wheezing/whistling breath and $100 or less in

the case of all other symptoms. Thus, the bids exceeding $5000 would

appear to be outliers and, in any case, their presence contributes to mean

original bids which are larger than corresponding ABM WTP estimates

reported in Tables 1 and 2.

Revised bids to avoid one day of ozone related symptoms were

calculated using equation (1)

RBi = Bi(RTME/ITME) (1)

where RB i denotes the revised bid for symptom i, B i denotes the original

bid for symptom i, RTME denotes respondent's revised total monthly

expenditures to eliminate (up to three) most bothersome symptoms, and ITME

denotes total monthly expenditures implied by the respondent's original

bids. Thus, the ratio used to compute RB i is specific to respondents but

not to symptoms. For a given respondent, each B i

 is adjusted using the

same ratio. A more precise procedure would have been to obtain adjustment

ratios for each symptom, however, this approach was ruled out in order to

keep the questionnaire as brief and simple as practicable. As shown in

16
TABLE 7. SUMMARY OF CVM BIDS TO AVOID SINUS PAIN OR

DISCOMFORT FOR ONE DAY

Original Bid

Distribution

Value Frequency

Revised Bid

Distribution

Revised Bid with Consistency

Distribution Check Exclusions

Value Frequency Value Frequency

$ .00 9

1.00 10

2.00 3

5.00 3

10.00 6

15.00 1

20.00 2

25.00 2

30.00 2

33.00 1

50.00 3

100.00 1

9999.00 1

Missing 1

Valid Cases

Mean

Median

Standard

Error

t-ratio

4 4

$239.50

3.50

228.49 0.26 0.487

1.05 3.62* 3.86*

$ .00 24

.09 1

.33 1

.36 1

.40 1

.42 1

.48 1

.63 3

1.19 1

1.64 1

1.67 1

2.62 1

2.69 1

2.86 1

3.33 2

4.71 1

6.02 1

7.14 1

Missing 1

44

$ .94

.00

$ .00 8

.33 1

1.19 1

1.64 1

1.67 1

2.62 1

2.69 1

2.86 1

3.33 2

4.71 1

6.02 1

7.14 1

Missing 1

2 0

$ 1.88

1.42

*Denotes significance at 5% level.

17
TABLE 8. SUMMARY OF CVM BIDS TO AVOID COUGH FOR ONE DAY

Original Bid Revised Bid

Distribution Distribution

Revised Bid

Distribution

with Consistency

Check Exclusions

Value Frequency Value Frequency Value Frequency

$ .00 14

1.00 4

10.00 1

15.00 1

20.00 3

25.00 1

35.00 1

50.00 3

9999.00 1

Missing 0

Valid Cases 2 9

Mean $ 355.10

Median 1.00

Standard

Error 344.45

t-ratio 1.03

$ .00 20 $ .00

2.14 1 2.14

2.48 1 2.48

2.86 1 2.86

3.11 1 3.11

3.33 3 3.33

4.71 1 4.71

6.67 1 6.67

9.52 1 9.52

Missing 1 Missing

2 8

$ 1.24

.00

.45

2.76*

$ 1.39

.00

.50

2.78*

17

1

1

1

1

1

1

1

1

1

*Denotes significance at 5% level.

18
TABLE 9. SUMMARY OF CVM BIDS TO AVOID THROAT IRRITATION FOR ONE DAY

Original Bid

Distribution

Value Frequency

Revised Bid

Distribution

Revised Bid with Consistency

Distribution Check Exclusions

Value Frequency Value Frequency

$ .00

1.00

5.00

10.00

20.00

25.00

50.00

100.00

Missing

8

5

1

6

1

2

1

2

0

Valid Cases

Mean $

Median

Standard

Error

t-ratio

26

15.00

3.00

5.40 .93

2.78* 1.68

$ .00 19

.75 1

1.43 1

2.86 1

3.11 1

3.33 1

6.52 1

24.10 1

Missing 0

26 17

$ 1.56 $ 2.43

.00 .00

$ .00 11

1.43 1

2.86 1

3.11 1

3.33 1

6.52 1

24.10 1

Missing 0

1.43

1.70

*Denotes significance at 5% level.

19
TABLE 10. SUMMARY OF CVM BIDS TO AVOID CHEST TIGHT FOR ONE DAY

Original Bid Revised Bid

Distribution Distribution

Revised Bid

Distribution

with Consistency

Check Exclusions

Value Frequency Value Frequency Value Frequency

$ .00 9

3.00 3

5.00 1

10.00 1

20.00 1

30.00 1

35.00 2

50.00 4

5000.00 2

9999.99 1

Missing 0

5

1

1

1

1

1

1

1

Valid Cases

Mean

Median

Standard

Error

t-ratio

25

$ 813.72

5.00

471.59 .96 1.82

1.73 2.45* 2.77*

$ .00 17

.81 1

1.04 1

7.14 1

8.43 1

9.57 1

14.29 1

15.00 1

Missing 1

2 4

$ 2.35

.00

$ .00

1.04

7.14

8.43

9.57

14.29

15.00

Missing

11

$5.04

1.05

*Denotes significance at 5% level.

20
TABLE 11. SUMMARY OF CVM BIDS TO AVOID COULD NOT BREATHE

DEEP FOR ONE DAY

Original Bid Revised Bid

Distribution Distribution

Revised Bid

Distribution

with Consistency

Check Exclusions

Value Frequency Value Frequency Value Frequency

$ .00 16

1.00 1

2.00 1

3.00 1

4.00 1

5.00 1

10.00 1

20.00 1

35.00 1

50.00 3

100.00 1

5000.00 1

9999.00 3

Missing 0

Valid Cases 3 2

Mean $1139.58

Median 1.00

Standard

Error 544.56

t-ratio 2.09*

$ .00 25

.81 1

1.04 1

1.43 1

3.08 1

7.14 1

14.29 1

25.00 1

Missing 0

3 2 1 7

$1.65 $3.06

.00 .00

.90 1.64

1.83 1.87

$ .00 11

1.04 1

1.43 1

3.08 1

7.14 1

14.29 1

25.00 1

Missing 0

*Denotes significance at 5% level.

21
TABLE 12. SUMMARY OF CVM BIDS TO AVOID PAIN ON DEEP BREATH FOR ONE DAY

Original Bid Revised Bid

Distribution Distribution

Revised Bid

Distribution

with Consistency

Check Exclusions

Value Frequency Value Frequency Value Frequency

$ .00 7

3.00 1

4.00 1

20.00 1

40.00 1

50.00 2

100.00 1

5000.00 1

9999.00 1

Missing 2

Valid Cases

Mean

Median

Standard

Error

t-ratio

16 1 6 8

$ 954.13 $ 2.65 $ 5.97

3.50 .00 2.08

678.33 1.60 3.11

1.41 1.66 1.92

$ .00 12 $ .00 4

4.17 1 4.17 1

7.14 1 7.14 1

11.43 1 11.43 1

25.00 1 25.00 1

Missing 2 Missing 0

22
TABLE 13. SUMMARY OF CVM BIDS TO AVOID OUT OF BREATH EASILY FOR ONE DAY

Original Bid Revised Bid

Distribution Distribution

Revised Bid

Distribution

with Consistency

Check Exclusions

Value Frequency Value Frequency Value Frequency

$ .00

1.00

2.00

3.00

10.00

50.00

Missing

9

1

1

1

2

2

1

Valid Cases

Mean

Median

Standard

Error

t-ratio

16 16 8

$ 7.88 $ .30 $ .60

.00 .00 .00

4.20 .26 .56

1.88 1.15 1.07

$ .00 14

.61 1

4.17 1

Missing 1

$ .00 6

4.17 1

Missing 1

23
TABLE 14. SUMMARY OF CVM BIDS TO AVOID WHEEZING/WHISTLING

BREATH FOR ONE DAY

Original Bid Revised Bid

Revised Bid

Distribution

with Consistency

Distribution Distribution Check Exclusions

Value Frequency Value Frequency Value Frequency

$ .00

2.00

5.00

35.00

50.00

500.00

Missing

5

1

1

1

2

1

0

Valid Cases

Mean $

Median

Standard

Error

t-ratio

11

58.36

2.00

44.59 1.41 2.34

1.31 1.21 1.17

$ .00 7

.54 1

2.14 1

14.29 1

Missing 1

10

$ 1.70

.00

$ .00 4

2.14 1

14.29 1

Missing 1

6

$ 2.74

.00

24
TABLE 15. SUMMARY OF CVM BIDS TO AVOID HEADACHE FOR ONE DAY

Original Bid

Distribution

Value Frequency

Revised Bid

Distribution

Revised Bid with Consistency

Distribution Check Exclusions

Value Frequency Value Frequency

$ .00 14

1.00 18

2.00 4

5.00 8

7.00 1

10.00 2

15.00 1

20.00 2

35.00 1

50.00 3

75.00 2

100.00 4

9999.00 1

Missing 1

Valid Cases

Mean

Median

Standard

Error

t-ratio

61 61 1 6

$ 178.39 $ 1.19 $ 4.35

1.00 .00 2.35

163.72 .42 1.32

1.09 2.83* 3.30*

$ .00 41

.04 1

.10 1

.18 1

.30 1

.38 1

.48 1

.63 2

.95 1

1.67 1

2.14 1

2.20 1

2.50 1

2.99 1

3.75 1

6.52 1

6.67 1

8.33 1

14.29 1

17.86 1

Missing 1

$ .00 4

.63 1

1.67 1

2.14 1

2.20 1

2.50 1

2.99 1

3.75 1

6.52 1

6.67 1

8.33 1

14.29 1

17.86 1

Missing 1

*Denotes significance at 5% level.

25
Tables 7-15, averages of revised bids always are lower, and frequently

dramatically lower, than averages of original bids. In the case of sinus

pain, for example, B i = $239.50 while RB i = $.94 and for headache, B i =

$178.39 while RBi = $1.19. A key reason for these striking results is that

confronting respondents with the implications of their original bids for

total monthly expenditure caused, in some cases, a complete reassessment of

WTP. The large outlier values present in the original bid vanish in the

frequency distributions of revised bids. In fact, the largest revised bid

calculated for any of the nine symptoms was $25! Yet, despite the

comparatively low values for revised bids, the null hypothesis that the

true mean bid equals zero would be rejected at the 5 percent level for

four of nine symptoms.

The revised bid values should be interpreted as lower bound estimates

of WTP to avoid one day of ozone-related symptoms. Rowe and Chestnut

(1986), in their analysis of southern California asthmatics who

participated in the UCLA CORD study, found that consistency checks applied

to contingent valuation data frequently provide a basis for discarding

ill-considered bids. The procedure used here to obtain revised bids

effectively eliminates WTP estimates that violate budget constraints; yet,

it does not identify inconsistencies such as low or zero bids to avoid

either severe symptoms or symptoms that prompted the respondent to take

averting action. As a consequence, Tables 7-15 present a third frequency

distribution for each symptom that shows the effects of discarding certain

low or zero bids. The consistency checks applied are:

(1) If symptom severity rank is 4 or 5 and the bid is $1 or less, the

bid is excluded.

26
(2) If averting action is undertaken to reduce the severity or

duration of a symptom and the bid is $1 or less, the bid is

excluded.

Admittedly, these criteria are somewhat arbitrary, but any consistency

checks used would suffer this problem. When applied to the revised bids,

they eliminate roughly half of the observations for each symptom and more

than half of the zero bids. Nevertheless, even with these comparatively

large number of exclusions, averages of revised bids by symptom remain low.

The range of these averages is $.60 to avoid one day of out of breath

easily to about $6.00 to avoid one day of pain on deep breath.

Averages of revised bids both before and after imposing consistency

checks are lower than corresponding WTP estimates reported in Tables 1 and

2 . As discussed more fully in Dickie et al., however, the ABM estimates

represent an upper bound to WTP. Averting goods or actions used in making

the ABM calculations in that study were: (1) automobile air conditioning,

(2) home air conditioning, (3) home air purification, and (4) switching

from a gas to an electric range for cooking. Each of these goods is likely

to be a source of direct utility in addition to reducing frequency or

severity of symptoms. These direct utility effects are included in the ABM

WTP calculations. In any case, the two sets of revised CVM estimates

presented here together with the ABM estimates indicate that averages of

raw or original CVM bids are likely to inflate estimates of WTP to avoid

ozone related symptoms for one day. Moreover, revising bids by confronting

respondents with their implied monthly total expenditures for symptom

avoidance, reconciles much of the absolute discrepancy between CVM and ABM

WTP estimates.

27
A further perspective on the revised bids can be obtained by examining

their relationships to other variables. Three approaches are used. First,

revised bids are cross tabulated by whether averting action was taken and

by symptom severity. Second, mean bids for each symptom were calculated

according to whether the respondent had impaired respiratory function.

Third, regressions were run to determine whether variation in revised bids

for particular symptoms can be explained by variables such as health status

(normal or respiratory impaired), income, averting actions, and symptom

severity. Both of these approaches reveal patterns in the revised bids

that are consistent with the theory elaborated in Dickie et al.

Table 16 shows cross tabulations of whether a respondent took averting

action to reduce severity or duration of a symptom by the amount of the

revised bid. The decimal fractions in the body of the table show the

proportion of respondents who reported taking an averting action and the

figures in parentheses show the number of observations in a cell. For

example, of the 20 individuals whose revised bids to avoid one day of cough

was $0-2, 15 percent took averting action such as using cough drops or

cough medicine. Proportions of respondents taking averting action tends to

rise with increases in the amount bid. There are only two exceptions to

this pattern and these occur in cases where there are two observations or

fewer in a cell. Apparently, if a symptom is bothersome enough to warrant

averting action, it also tends to warrant a larger bid.

The connection between symptom severity and averting behavior is

examined more carefully in Table 17. The entries in the body of this table

are interpreted in the same way as in Table 16. Thus, of the 17 persons

experiencing sinus pain, 82.4 percent took averting action such as using a

28
TABLE 16. CROSS TABULATION OF MITIGATION BY BID

Bid

Symptom $0-2 $2-10 $10-25 Overall

Sinus Pain .667 (36) .875 (8) ---a

Cough .150 (20) .750 (8) ---a

Throat Irritation .476 (21) 1.00 (4) 1.00 (1)

Chest Tight .579 (19) 1.00 (3) 1.00 (2)

Could Not Breathe Deep .536 (28) .500 (2) 1.00 (2)

Pain on Deep Breath .417 (12) 1.00 (2) 1.00 (2)

Out of Breath Easily .533 (15) 1.00 (1) ---a

Wheezing/Whistling Breath .500 (8) .000 (1) 1.00 (1)

Headache .882 (51) 1.00 (8) 1.00 (2)

.705 (44)

.344 (28)

.577 (26)

.667 (24)

.563 (32)

.562 (16)

.562 (16)

.500 (10)

.901 (61)

aDenotes no bids in this category.

29
TABLE 17. CROSS TABULATION OF MITIGATION BY SYMPTOM SEVERITY

Severity Rank

Symptom 1 2 3 4 5 Overall

Sinus Pain .000 (2) .444 (9) .824 (17) .786 (14) 1.000 (3) .711 (45)

Cough .200 (5) .222 (9) .462 (13) .000 (1) 1.000 (1) .344 (29)

Throat Irritation .333 (3) .500 (8) .333 (6) .875 (8) 1.000 (1) .577 (26)

Chest Tight 1.000 (1) .571 (7) .500 (4) .727 (11) 1.000 (1) .667 (24)

Could Not Breathe Deep --- a .500 (6) .385 (13) .727 (11) 1.000 (2) .563 (32)

Pain on Deep Breath --- a .667 (3) .400 (5) .700 (10) --- a .500 (18)

Out of Breath Easily a --- .000 (1) .454 (11) .800 (5) --- a .529 (17)

Wheezing/Whistling Breath .400 (5) .000 (2) 1.000 (1) 1.000 (2) 1.000 (1) .545 (11)

Headache .750 (4) .818 (11) .895 (19) .957 (23) 1.000 (5) .903 (62)

a

Denotes no bids in this category.

30
nasal decongestant or pain relievers including aspirin or acetaminophen.

Again an expected pattern emerges: averting action is likely if symptoms

are perceived as more severe. Exceptions can be noted particularly in

situations where severity rank equals three. Nevertheless, when severity

rank equals four or five, proportions of respondents taking averting action

are almost always larger than when severity is ranked one or two.

Table 18 separately calculates mean revised bids for normal and

respiratory impaired respondents. As discussed in Dickie et al. (1986),

respiratory impaired respondents are those with physician diagnosed asthma,

bronchitis, emphysema, or other lung disease. All other respondents are

classified in the normal subsample. Interestingly, the mean revised bids

for the impaired group are no larger than those in the normal subsample for

all symptoms except wheezing/whistling breath and chest tight. This same

relationship between WTP for symptom avoidance was observed using the ABM

(compare Tables 1 and 2) and was explained based on differences in the

symptom production functions of the two groups by Dickie et al. (see

Chapter 1, pp. 10-14). Briefly, even though the marginal cost schedule for

symptom avoidance for the impaired group lies above that for the normal

group, WTP for the normal group still may be lower if impaired respondents

experience symptoms more frequently.

Preliminary regression results to explain the variation in revised

bids for each of the nine ozone related symptoms are presented in Table 19.

Explanatory variables used are defined below:

RANK= Severity of last occurrence of symptom on a 1-5 scale; 1

denotes least severity, 5 denotes greatest severity.

31
TABLE 18. MEANS OF CONTINGENT VALUATION METHOD BIDS TO AVOID SYMPTOMS

FOR NORMAL AND RESPIRATORY IMPAIRED RESPONDENTS

Symptom

Normal Budget Impaired Budget

Constraint Bid Constraint Bid

Sinus Pain

Cough

Throat Irritation

Chest Tight

Could Not Breathe Deep

Pain on Deep Breath

Out of Breath Easily

Wheezing/Whistling Breath

Headache

$1.11 $.59

1.70 .31

2.22 .73

1.30 3.61

1.83 1.43

3.11 .00

.00 .00

.43 2.97

1.26 .60

32
33

TABLE 19. REGRESSION RESULTS: REVISED CONTINGENT VALUATION BIDS USED

AS DEPENDENT VARIABLES

(t-statistics in parentheses)

Symptom RANK ACT EFFECT FREQ IMPAIR INCFAM

Number of

Constant R* Observations

Sinus Pain

Cough

Throat Irritation

Chest Tight

Could Not Breathe Deep

Pain on Deep Breath

Out of Breath Easily

Wheezing/Whistling Breath

Headache

-.212 .528 .774 -.00817 -.622 -.00211 2.45

(-.659) (.639) (.800) (-.241) (-.937) (-.135) (1.77)

.239 2.83 -2.76 -.00142 -.965 -.00304 1.93

(.445) (2.67) (-1.86) (-.343) (-.964) (-1.26) (1.02)

1.501 4.185 -2.11 -.0396 -1.56 .00299 -4.12

(1.29) (1.33) (-.513) (-.837) (-.683) (.507) (-.877)

-.592 8.42 -6.98 -.00828 2.47 -.000174 .930

(-.621) (2.88) (-1.93) (-.625) (1.05) (-.032) (.157)

-1.03 7.24 -6.60 -.00201 -2.15 -.00370 5.89

(-.700) (1.97) (-1.53) (-.160) (-.878) (-.788) (1.09)

2.033 1.71 1.06 .0751 -2.07 -.026 8.15

(.677) (.215) (.108) (.964) (-.397) (-2.204) (.652)

.832 -.608 -2.57 -.00159 ---* -.00312

(1.14) (-.551) (-2.35) (-.482) (-.965) (.094)

1.42 12.10 -8.101 -.0457

(.653) (.543) (-.458) (-.749)

.767 .782

(1.53) .327

-2.71

(-.138)

-.00252

(-.2951

---*

-.594 .000837

(-.596) (.221)

-.0036 1.31

(-.246) (.112)

.263 .69

-1.97

(-.705)

.14 40

.45 26

.51 24

.49 22

.24 28

.54

.54

.08

15

10

10

55

*Variable could not be entered in equation because of correlation problems.
ACT = 1 if respondent took averting action to relieve symptom, 0

otherwise.

EFFECT = Difference between initial severity rank and severity rank

after averting action was taken divided by initial severity

rank. Was set equal to zero if no averting action was taken.

FREQ = Annual frequency of symptom occurrence.

IMPAIR = 1 if respondent is in impaired subsample, 0 otherwise.

INCFAM = Family income of respondent.

Coefficients of RANK, ACT, and INCFAM are expected to be positive.

Respondents with more severe symptoms, who are bothered enough to take

averting action, and who have greater financial resources are likely to

have greater WTP to avoid symptoms. Coefficients of EFFECT and FREQ on the

other and are expected to be negative. Greater reductions in severity;

that is, larger values of EFFECT, due to averting actions are likely to

lead to lower WTP. This relationship can be established by referring to

the model underlying the ABM, which indicates that WTP equals marginal cost

of symptom avoidance. Marginal cost, in turn, equals the unit cost of an

averting good divided by its marginal productivity in reducing symptoms.

If marginal productivity of averting actions is low (or zero, implying that

such actions are not worth undertaking), WTP would be comparatively large.

Additionally, assuming constant costs of averting actions and diminishing

marginal productivity in reducing symptoms, WTP should decrease with FREQ.

After adjusting for symptom frequency, the sign of the coefficient of

IMPAIR should be positive. In other words, given the same frequency of

symptom occurrence, respiratory impaired individuals have higher marginal

costs of symptom avoidance and, therefore, larger WTP.

The preliminary regression results in Table 19 indicate that, overall,

performance of the nine equations is not particularly strong. Two of the

34
equations have low R 2

 values (sinus pain, R 2 = .14 and headache, R 2 = .08)

and the null hypothesis of no linear relation between the dependent

variable and all explanatory variables cannot be rejected at the 5 percent

level. Three other regressions, those for pain on deep breath, out of

breath easily, and wheezing/whistling breath are based on 15 or fewer

observations. Nevertheless, in the out of breath easily equation, the

coefficient of EFFECT is negative and significantly different from zero at

the 5 percent level. Explanatory variables perform somewhat better in the

remaining four equations. The coefficient of RANK has the expected sign

(positive) and is significantly different from zero at the 10 percent level

using a one-tail test in the throat irritation equation. The coefficients

of ACT are positive and significant at the 10 percent level or lower using

a one-tail test in equations for cough, chest tight, throat irritation and

cannot breathe deep. Coefficients of EFFECT are negative and significant

at 10 percent using a one-tail test in equations for cough, chest tight and

cannot breathe deep. Coefficients of FREQ, IMPAIR, and INCFAM never

attained even marginal significance levels with expected signs.

Further empirical work to refine these regression estimates is

continuing. As a consequence, the results presented in Table 19 are

preliminary and used advisedly. Three econometric issues presently are

being explored. First, the equations were estimated using ordinary least

squares even though a significant percentage of dependent variable values

were zero. Limited dependent variable estimation methods, such as tobit,

would be more appropriate. Second, the estimates do not account for the

sample selection bias problem discussed earlier. Third, estimation

efficiency might be improved using seeming unrelated regressions, although

35
a possible difficulty in applying this approach involves the different

numbers of observations in each equation. In any case, more refined

regression estimates can be made available to USEPA later in spring, 1987.

5 . SUMMARY AND CONCLUSIONS

The main purpose of this report is to reconcile differences between

contingent valuation method (CVM) and averting behavior method (ABM)

estimates of willingness to pay (WTP) to avoid health symptoms of ozone

exposure including chest tightness, throat irritation, headache, and pain

on deep breath. Average CVM bids to avoid one day of these symptoms

frequently exceed their ABM counterparts by factors between five and ten.

As a result, policy makers are left with inadequate guidance concerning the

health benefits of ozone control. The reconciliation approach used in this

report focuses on obtaining revised bids in a contingent valuation

framework. After obtaining WTP to avoid one day's experience with up to

three bothersome symptoms, interviewers calculate implications of these

bids for total monthly expenditures by multiplying the bid times frequency

of occurrence. Respondents confronted with these monthly total expenditure

figures often make substantial downward revisions in their original bids.

For example, original bids to avoid one day of headache averaged $178.39,

whereas revised bids averaged $1.19; original bids to avoid one day of

cough averaged $355.10 whereas revised bids averaged $1.19. These results

suggest that in CVM studies of frequently occurring events such as health

symptoms, care should be taken to ensure that respondents are aware of

total expenditure implications of their bids. Moreover, revised bids to

eliminate all nine ozone symptoms considered are lower than ABM estimates

reported in Dickie et al. (1986). This relationship is expected because

36
ABM overestimates WTP; in addition to reducing symptoms, averting goods

used in the ABM calculations may represent sources of direct utility.

Thus, to avoid one day of frequently occurring ozone-related health

symptoms, WTP is effectively bounded.

37
REFERENCES

Bartik, T. 1986. "Evaluating the Benefits of Non-Marginal Reductions in

Pollution Using Information on Defensive Expenditures," mimeo,

Department of Economics, Vanderbilt University, Nashville, TN.

Berger, M.,G. Blomquist, D. Kenkel, and G. Tolley. 1985. "Valuing

Changes in Health Risks: A Comparison of Alternative Measures,"

mimeo, Department of Economics, University of Kentucky, Lexington, KY.

Bockstael, N. and R. McConnell. 1983. "Welfare Measurement in the

Household Production Framework," American Economic Review 73: 806-814.

Chestnut, L and D. Violette. 1984. "Estimates of Willingness to Pay for

Pollution-Induced Changes in Morbidity: A Critique for Benefit Cost

Analysis of Pollution Regulation," EPA-68-01-6543.

Courant, P. N. and R. C. Porter. 1981. "Averting Expenditure and the Cost

of Pollution," Journal of Environmental Economics and Management 8:

321-329.

Detels, R., S. Rokaw, A. Coulson, D. Tashkin, J. Sayre and F. Massey, Jr.

1979. "The UCLA Population Studies of Chronic Obstructive Respiratory

Disease I. Methodology," American Journal of Epidemiology 109: 33-58.

Detels, R., J. Sayre, A. Coulson, et al. 1981. "The UCLA Population

Studies of Chronic Obstructive Respiratory Disease IV. Respiratory

Effects of Long Term Exposure to Photochemical Oxidants," American

Review of Respiratory Disease 124: 673-680.

38
Dickie, M. 1987. "Value of Symptoms of Ozone Exposure: An Application

of the Averting Behavior Method," unpublished Ph.D. dissertation

(Laramie, WY: The University of Wyoming), May.

Dickie, M., S. Gerking, W. Schulze, A. Coulson, and D. Tashkin. 1986.

"Value of Symptoms of Ozone Exposure: An Application of the Averting

Behavior Method," in Improving Accuracy and Reducing Costs of

Environmental Benefit Assessments, U.S. Environmental Protection

Agency, Washington, D.C. (September).

Gerking, S., A. Coulson, W. Schulze, D. Tashkin, D. Anderson, M. Dickie,

and D. Brookshire. 1984. "Estimating Benefits of Reducing Community

Low-Level Ozone Exposure: A Feasibility Study," in Experimental

Methods for Assessing Environmental Benefits, Volume 3, U.S.

Environmental Protection Agency, Washington, D.C. (March).

Gerking, S. and L. Stanley. 1986. "An Economic Analysis of Air Pollution

and Health: The Case of St. Louis," Review of Economics and

Statistics 68: 115-121.

Harford, J. D. 1984. "Averting Behavior and the Benefits of Reduced

Soiling," Journal of Environmental Economics and Management 11:

296-302.

Harrington, W. and P. R. Portney. 1987. "Valuing the Benefits of Health

and Safety Regulation in the Presence of Defensive Expenditures,"

Journal of Urban Economics, forthcoming.

39
Loehman, E., S. Berg, A. Arroyo, R. Hedinger, J. Schwartz, M. Shaw, R.

Fahien, V. De, R. Fishe, D. Rio, W. Rossley, and A. Green. 1979.

"Distributional Analysis of Regional Benefits and Cost of Air Quality

Control," Journal of Environmental Economics and Management 6:

222-243.

Rowe, R. D. and L. G. Chestnut. 1986. "Valuing Changes in Morbidity:

WTP Versus COI Measures," mimeo, Energy and Resource Consultants,

Inc., Boulder, CO.

40
APPENDIX A

REVISED FOLLOW-UP QUESTIONNAIRE

UCLA/WYOMING OZONE STUDY

Revised Follow-Up Questionnaire

R.I.D.#

1-7

Respondents Name Form type 21

8 9

Record # 01

10-11

Interviewer I.D.

Date

Time beginning

Length of Interview

1 2

13-16

1-7

21-22

INTERVIEWER: PLEASE ASK THE RESPONDENT IF THEY HAVE

THEIR COPY OF THE PURPLE SYMPTOM SEVERITY

SCALE THAT WAS SENT TO THEM WITH THEIR

LETTER. Yes No

IF THEY DO NOT HAVE THE SCALE INSTRUCT THEM

TO GET A PIECE OF PAPER AND PENCIL AND HELP

THEM REPRODUCE THE SCALE TO USE DURING THE

INTERVIEW.

IF THEY HAVE THE SCALE PROCEED WITH THE INTERVIEW.

1. Have you moved since we talked to you last?

yes

n o

2. Have you changed jobs ? yes

n o

IF "YES" TO EITHER QUESTION-FILL OUT APPENDIX: IF "NO" TO

BOTH QUESTIONS PROCEED WITH THE INTERVIEW.

41
FIRST I °D LIKE TO READ YOU A LIST OF SYMPTOMS OTHER PEOPLE SOMETIMES HAVE. AS

I READ EACH ONE, PLEASE TELL ME IF IT HAS BOTHERED YOU ANYTIME IN THE PAST MONTH

(THE MONTH ENDING TODAY).

YES Did you have this: Thinking about the times NO

you had this symptom in

the past month, did It

bother you:

In the day before a great very

last yesterday yesterday deal moderate mildly

month

yes n o yes n o

1

1 . Did your eyes 1 1 2 1 2 3 2

feel irritated?

2. Did you feel that 1 1 2 1 2 3 2

you could not see

as well as usual?

3 . Were your eyes 1 1 2 1 2 3 2

unusually sensitive to bright

light?

4. Did you have a 1 1 2 1 2

ringing in your

ears?

5. Did you have pain 1 1 2 1 2

in your ears? 43-47

6. Did you have

sinus pain or

1 1 2 1 2

discomfort?

7. Did you have a 1 1 2 1 2

nosebleed?

8 . Was your nose dry 1 1 2 1 2

and painful?

9. Was your nose 1 1 2 1 2

runny?

3

3

3

3

3

3

2

2

2

2

2

2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

23-27

28-32

33-37

38-42

48-52

53-57

58-62

63-67

42
YES Did you have this: Thinking about the times NO

you had this symptom In

the past month, did It

bother you:

In the day before a great very

last yesterday yesterday deal moderate mildly

month

yes no yes

10. Did you have 1 1 2 1 2 3 2 1 2

a cough?

11. Was your throat 1 1 2 1 2 3 2 1 2

irritated? 73-77

1-9

02

10-11

12-16

12. Was your voice 1 1 2 1 2 3 2 1 2

husky or did you

lose your voice?

13. Did you bring up 1 1 2 1 2 3 2 1 2

phlegm, sputum or

mucous from your

chest?

14. Did your chest 1 1 2 1 2 3 2 1 2

feel tight?

15. Did you feel that 1 1 2 1 2 3 2 1 2

you could not take

a deep breath?

16. Did you have pain 1 1 2 1 2 2 2 1 2

when you took a

deep breath?

17. Did you get out 1 1 2 1 2 3 2 1 2

of breath easily?

no

68-72

17-21

22-26

27-31

32-36

37-41

18. Did your breath- 1 1 2 1 2 3 2 1 2

ing sound wheezing or whistling

42-46

2

4 3
YES Did you have this: Thinking about the times NO

you had this symptom in

the past month, did it

bother you:

in the day before a great very

last yesterday yesterday deal moderate mildly

month

yes no yes no

19. Did you feel

that your heart

was beating very

fast at times

when you were

resting?

20. Did you get tired

easily?

21. Did you feel

faint or dizzy?

22. Did you feel

spaced out or

disoriented?

1 1

1 1

1 1

1 1

1 1

1 1

1 1

1 1

23. Did you have a

headache?

24. Did you have

chills or fever?

(which?)

-------- 1-9

03

10-11

25. Did you feel

nauseated (sick

to your stomach)?

26. Did you have

swollen glands?

2 1 2 3

2 1 2 3

2 1 2 3

2 1 2 3

2 1 2 3

2 1 2 3

2 1 2 3

2 1 2 3

2 1

2 1

2 1

2 1

2 1

2 1

2 1

2 1

2

2

2

2

2

2

2

2

47-51

52-56

57-61

62-66

67-71

72-76

12-16

17-21

3

4 4
IF THERE ARE NO SYMPTOMS:

GO TO THE END OF THE QUESTIONNAIRE - AND OBTAIN SOCIAL SECURITY NUMBER

AFTER THE LIST IS COMPLETE, CHECK FOR THE HIGHEST LEVELS OF RESPONSE FOR

SYMPTOMS MARKED WITH AN ASTERISK LOCK AT THE PERCIEVED SEVERITY SCALE RESPONSES

AND CHOOSE THOSE THREE WHICH HAVE THE HIGHEST VALUES. IF THERE ARE MORE THAN

THREE SYMPTOMS WITH EQUALLY HIGH VALUES, ASK QUESTION 2 BELOW.

IF THERE IS AT LEAST ONE SYMPTOM BUT LESS THAN THREE SYMPTOMS:

GO TO Q3.

Q2. We want to concentrate only on those symptoms that have bothered you the

most during the past month. Of the following symptoms (READ LIST OF

CONTENDERS) which three were the most bothersome for you in the past month?

1.

2 .

3 .

Q3. Now, I would like to ask you some questions about these symptoms. W e

are interested in:

1. how often they happen

2. how much discomfort or bother they cause you and

3. what you do to make yourself feel better when you have these

symptoms.

We’ll start with the first symptom on the list which is [SYMPTOM 1].

THE SET OF QUESTIONS WHICH FOLLOW ARE TO BE ASKED FOR EACH OF THE THREE

SYMPTOMS LISTED ABOVE IN QUESTION 2. ASK THE ENTIRE SET: OF QUESTIONS FOR

SYMPTOM 1, THEN REPEAT THIS PROCEDURE FOR SYMPTOM 2, THEN SYMPTOM 3.

SYMPTOM 1

Q3a. How many days in the past month did you have -- SYMPTOM

DAYS

22-23

24-25

4

45
Q3b. About how many days during the past year did you experience this

symptom?

DAYS

Q3c. Sometimes people experience symptoms more or less often during

different seasons of the year. Please the ink about the past year, from

July 1985 to the present. During the past month, did you experience

[SYMPTOM] more often, about the same number of times or less often than

in the months of:

Q3c.1 During June, July and August of 1985?

(summer)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

Q3c.2 During September, October and November of 1985?

(fall)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

Q3c.3 During December, January and February of 1985-1986?

(winter)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

Q3c.4 During March, April and May of 1986?

(spring)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

31

3 2

3 3

Q3d. Now, looking at the scale, labeled symptom severity, notice that

the value 1 stands for very little discomfort or bother - where you

just barely know the symptom is there and, at the other end, the

number 5 stands for maximum discomfort or bother.

Q3d.1 Using this scale, how would you rank the amount of discomfort or

bother you had the last time you experienced [SYMPTOM] ?

26-28

2 9

3 0

RANK ----------------------

5

46
Q3d.2 Using this scale, how would you rank the amount of discomfort or

bother you had when it was the worst episode of [SYMPTOM] in the last

month?

RANK -----------------------------------

Q3d.3 Using the symptom severity scale that we used before, how severe

was this symptom last summer: the months of June, July and August of

1985?

RANK --------------------------------

Q3d.4 Using the symptom severity scale that we used before, how severe

was this symptom last fall; the months of September, October and

November of 1985?

RANK ---------------------------------------

Q3d.5 Using the symptom severity scale that we used before, how severe

was this symptom last winter: the months of December, January and

February of 1985-1096?

RANK ---------------------------------------

34

35

3 6

3 7

3 8

3 9

Q3d.6 Using the symptom severity scale that we used before, how severe

was this symptom last spring; the months of March, April and May?

RANK -----------------------------------------

People who are bothered by symptoms sometimes take actions to relieve them.

For example:

- someone may see a doctor or

- take medication prescribed by a doctor or

- take a nonprescription medication or

- stay home from work or

- limit their activities to only those that are the most important - or do

something else

when they are bothered by a symptom.

Q3e.1. The last time you experienced [SYMPTOM] did you do anything or

take any action at all to relieve you discomfort or bother from it?

(1) YES

(2) N o

6

47
Q3e.2. please tell me what you did.

RECORD THE RESPONSE ON THE FOLLOWING PAGE.

[INTERVIEWER, THE NEXT QUESTION REFERS TO SPECIFIC PROBES ON PAGE

8 OF THIS QUESTIONNAIRE. DIFFERENT SYMPTOMS HAVE DIFFERENT PROBES.

LOCK UP SYMPTOM ONE ON THE PROBE SHEET AND ASK THE ENTIRE QUESTION

ACCORDING TO IT°S CONTENT.]

Q3e.3. For [SYMPTOM], people sometimes take actions such as [LIST FOR

SYMPTOM]. Did you do any of these to relieve [SYMPTOM] this past

month?

Q3e.4. When [SYMPTOM] was the worst it was during this past month, did

you take any action to relieve your discomfort or bother?

(1) YES

(2) NO

Q3e.5. Please tell me what you did.

RECORD THE RESPONSE ON THE FOLLOWING PAGE. FOLLOW THE ENTRY WITH A (W).

[INTERVIEWER, THE NEXT QUESTION ALSO REFERS TO SPECIFIC PROBES ON PAGE

8 OF THIS QUESTIONNAIRE SO USE THE PROBE SHEET FOR THIS TOO.]

Q3e.6. For [SYMPTOM], people sometimes take actions such as [LIST FOR

SYMPTOM]. Did you do any of these to relieve [SYMPTOM] when it was the

worst that it was during the past month?

7

48

4 0
SYMPTOM 1 

POSSIBLE ACTIONS TO RELIEVE SYMPTOMS 

SYMPTOMS & 

POSSIBLE 

ACTIONS 

LAST WORST 

YES NO YES NO RESPONDENT°S WORDS FOR ACTION 

41-44 

45-46 

47-54 

EYES 

eye drops 

sunglasses 

EAR 

ear drops 

NOSE AND SINUS 

inhalent 

ice packs 

humidifier 

dehumidifier 

THROAT 

cough medicine 

drink hot liquids 

throat lozenges 

decongestants 

BREATHING 

broncho dialator 

respirator 

air purifier/ 

conditioner 

HEART 

rest 

limit activates 

OTHER 

over-the-counter medicine 

such aspirin 

consult physician 

use prescription 

or non-prescription medicine 

rest 

stay indoors 

heat pads 

cold compresses 

55-62 

63-68 

69-72 

1-9 

04 

10-11 

12-25 

26-35 

36-45 

8 

49 
Q3f. Think about the last time you did [ACTION] to relieve

[SYMPTOM]. After you did this, how would you rank the amount of discomfort

or bother you experienced from [SYMPTOM] on the 1 - 5 severity scale?

RANK 46

ONLY ASK Q3g IF RESPONDENT SAID HE/SHE TOOK [ACTION] WHEN [SYMPTOM] WAS

THE WORST. THIS MAY BE THE SAME TIME REFERRED TO IN Q3f ABOVE.

Q3g. Think about when [SYMPTOM] was the worst that it was last month.

After you did [ACTION] how would you rank the amount of discomfort or

bother you experienced from [SYMPTOM] on the 1 - 5 severity scale?

RANK 47

Think about the last time in the past month when you had

[SYMPTOM]. Suppose it had been possible to pay a sum of money to

have eliminated [SYMPTOM] immediately that one time. What sum of

money would you have been willing to pay?

We are not talking about getting rid of [SYMPTOM] forever; we are

talking about the amount of money you would have been willing to

pay to have eliminated the symptom that one time.

FURTHER EXPLANATION:

Think of this as the price of a special treatment that would

prevent the symptom one time. How high a price would you have

been willing to pay to eliminate the symptom this one time?

Q3h. What sum of money would you have been willing to pay?

AMOUNT 48-51

9

50
SYMPTOM 2

Q3a. How many days in the past month did you have -- SYMPTOM

DAYS

52-53

54-55

Q3b. About how many days during the past year did you experience this

symptom?

DAYS 56-58

Q3c. Sometimes people experience symptoms more or less often during

different seasons of the year. Please think about the past year, from

July 1985 to the present. During the past month, did you experience

[SYMPTOM] more often, about the same number of times or less often than

in the months of:

Q3c.1 During June, July and August of 1985?

(summer)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN 59

Q3c.2 During September, October and November of 1985?

(fall)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

60

Q3c.3 During December, January and February of 1985-1986?

(winter)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

61

Q3c.4 During March, April and May of 1986?

(spring)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN 62

10

51
Q3d. Now, looking at the scale, labeled symptom severity, not ice that

the value 1 stands for very little discomfort or bother - where you

just barely know the symptom is there and, at the other end, the

number 5 stands for maximum discomfort or bother.

Q3d.1 Using this scale, how would you rank the amount of discomfort or

bother you had the last time you experienced [SYMPTOM] ?

RANK

Q3d.2 Using this scale, how would you rank the amount of discomfort or

bother you had when it was the worst episode of [SYMPTOM] in the last

month?

RANK

Q3d.3 Using the symptom severity scale that we used before, how severe

was this symptom last summer: the months of June, July and August of

1985?

RANK

Q3d.4 Using the symptom severity scale that we used before, how severe

was this symptom last fall; the months of September, October and

November of 1985?

6 3

6 4

6 5

6 6

6 7

6 8

RANK

Q3d.5 Using the symptom severity scale that we used before, how severe

was this symptom last winter; the months of December, January and

February of 1985-1096?

RANK

Q3d.6 Using the symptom severity scale that we used before, how severe

was this symptom last spring; the months of March, April and May?

RANK

Q3.e People who are bothered by symptoms sometimes take actions to relieve them.

For example:

- someone may see a doctor or

- take medication prescribed by a doctor or

- take a nonprescription medication or

- stay home from work or

- limit their activities to only those that are the most important - or do

something else

when they are bothered by a symptom.

11

52
Q3e.1. The last time you experienced [SYMPTOM] did you do anything or

take any action at all to relieve you discomfort or bother from it?

(1) YES

(2) NO

Q3e.2. please tell me what you did.

RECORD THE RESPONSE ON THE FOLLOWING PAGE.

[INTERVIEWER, THE NEXT QUESTION REFERS TO SPECIFIC PROBES ON PAGE

13 OF THIS QUESTIONNAIRE. DIFFERENT SYMPTOMS HAVE DIFFERENT PROBES.

LOOK UP THIS RESPONDENT°S SECOND SYMPTOM ON THE PROBE SHEET AND ASK

THE ENTIRE QUESTION ACCORDING TO IT°S CONTENT.]

6 9

7 0

Q3e.3. For [SYMPTOM], people sometimes take actions such as [LIST FOR

SYMPTOM]. Did you do any of these to relieve [SYMPTOM] this past

month?

Q3e.4. When [SYMPTOM] was the worst it was during this past month, did

you take any action to relieve your discomfort or bother?

(1) YES

(2) No

Q3e.5. Please tell me what you did.

RECORD THE RESPONSE ON THE FOLLOWING PAGE. FOLLOW THE ENTRY WITH (W).

[ INTERVIEWER THE NEXT QUESTION ALSO REFERS TO SPECIFIC PROBES ON PAGE

13 OF THIS QUESTIONNAIRE SO USE THE PROBE SHEET FOR THIS TOO.]

Q3e.6. For [SYMPTOM], people sometimes take actions such as [LIST FOR

SYMPTOM]. Did you do any of these to relieve [SYMPTOM] when it was the

worst that it was during the past month?

12

53
\\
Q3f. Think about the last time you did [ACTION] to relieve

[SYMPTOM]. After you did this, how would you rank the amount of

discomfort or bother you experienced from [SYMPTOM] on the 1 - 5

severity scale?

RANK

ONLY ASK Q3g IF RESPONDENT SAID HE/SHE TOOK [ACTION] WHEN [SYMPTOM] WAS

THE WORST. THIS MAY BE THE SAME TIME REFERRED TO IN Q3f ABOVE.

Q3g. Think about when [SYMPTOM] was the worst that It was last month.

After you did [ACTION] how would you rank the amount of discomfort or

bother you experienced from [SYMPTOM] on the 1 - 5 severity scale?

RANK

Think about the last time in the past month when you had

[SYMPTOM]. Suppose It had been possible to pay a sum of money to

have eliminated [SYMPTOM] immediately that one time. What sum of

money would you have been willing to pay?

We are not talking about getting rid of [SYMPTOM] forever: we are

talking about the amount of money you would have been willing to

pay to have eliminated the symptom that one time

FURTHER EXPLANATION:

Think of this as the price of a special treatment that would

prevent the, symptom one time. How high a price would you have

been willing to pay to eliminate the symptom this one time?

Q3h. What sum of money would you have been willing to pay?

14

55
SYMPTOM 3

Q23a. How many days in the past month did you have -- SYMPTOM

DAYS

Q3b. About how many days during the past year did you experience this

symptom?

DAYS

Q3c. Sometimes people experience symptoms more or less often during

different seasons of the year. Please think about the past year, from

July 1985 to the present. During the past month, did you experience

[SYMPTOM] more often, about the same number of times or less often than

in the months of:

Q3c.1 During June, July and August of 1985?

(summer)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

Q3c.2 During September, October and November of 1985?

(fall)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

Q3c.3 During December, January and February of 1985-1986?

(winter)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

Q3c.4 During March, April and May of 1986?

(spring)

(1) MORE OFTEN

(2) SAME

(3) LESS OFTEN

1 5

56
Q3d. Now, looking at the scale labeled symptom severity notice that

the value 1 stands for very little discomfort or bother - where you

just barely know the symptom is there and, at the other end, the

number 5 stands for maximum discomfort or bother.

Q3d.1 Using this scale, how would you rank the amount of discomfort or

bother you had the last time you experienced [SYMPTOM] ?

2 3

Q3d.2 Using this scale, how would you rank the amount of discomfort or

bother you had when it was the worst episode of [SYMPTOM] In the last

month?

2 4

Q3d.3 Using the symptom severity scale that we used before, how severe

was this symptom last summer: the months of June, July and August of

1985?

Q3d.4 Using the symptom severity scale that we used before, how severe

was this symptom last fall; the months of September, October and

November of 1985?

Q3d.5 Using the symptom severity scale that we used before, how severe

was this symptom last winter; the months of December, January and

February of 1985-1096?

2 5

2 6

2 7

Q3d.6 Using the symptom severity scale that we used before, how severe

was this symptom last spring; the months of March, April and May?

2 8

Q3.e People who are bothered by symptoms sometimes take actions to relieve them.

For example:

- someone may see a doctor or

- take medication prescribed by a doctor or

- take a nonprescription medication or

- stay home from work or

- limit their activities to only those that are the most important -or do

something else

when they are bothered by a symptom.

16

57
Q3e.1. The last time you experienced [SYMPTOM] did you do anything or

take any action at all to relieve you discomfort or bother from it?

(1) YES

(2) NO

[ASK FOR ALL SYMPTOMS REGARDLESS OF THE VALUE ASSIGNED ON THE

SEVERITY SCALE]

Q3e.2. please tell me what you did.

RECORD THE RESPONSE ON THE FOLLOWING PAGE.

[INTERVIEWER, THE NEXT QUESTION REFERS TO SPECIFIC PROBES ON PAGE 18 OF THIS

QUESTIONNAIRE. DIFFERENT SYMPTOMS HAVE DIFFERENT PROBES. LOOK UP THIS

RESPONDENT"S THIRD SYMPTOM ON THE PROBE SHEET AND ASK THE ENTIRE QUESTION

ACCORDING TO lT"S CONTENT.]

Q3e.3. For [SYMPTOM], people sometimes take actions such as [LIST FOR

SYMPTOM]. Did you do any of these to relieve [SYMPTOM] this past

month?

Q3e.4. When [SYMPTOM] was the worst it was during this past month, did

you take any action to relieve your discomfort or bother?

(1) YES

(2) No

Q3e.5. Please tell me what you did.

RECORD THE RESPONSE ON THE FOLLOWING PAGE. FOLLOW THE ENTRY WITH (W)>

[INTERVIEWER, THE NEXT QUESTION ALSO REFERS TO SPECIFIC PROBES ON PAGE

18 OF THIS QUESTIONNAIRE SO USE THE PROBE SHEET FOR THIS TOO.]

Q3e.6. For [SYMPTOM], people sometimes take actions such as [LIST FOR

SYMPTOM]. Did you do any of these to relieve [SYMPTOM] when it was the

worst that it was during the past month?

29

3 0

17

58
59
Q3f. Think about the last time you did [ACTION] to relieve

[SYMPTOM]. After you did this, how would you rank the amount of

discomfort or bother you experienced from [SYMPTOM] on the 1 - 5

severity scale?

RANK

ONLY ASK Q3g IF RESPONDENT SAID HE/SHE TOOK [ACTION] WHEN [SYMPTOM] WAS

THE WORST. THIS MAY BE THE SAME TIME REFERRED TO IN Q3f ABOVE.

Q3g. Think about when [SYMPTOM] was the worst that It was last month.

After you did [ACTION] how would you rank the amount of discomfort or

bother you experienced from [SYMPTOM] on the 1 - 5 severity scale?

RANK

Think about the last time in the past month when you had

[SYMPTOM]. Suppose It had been possible to pay a sum of money to

have eliminated [SYMPTOM] immediately that one time. What sum of

money would you have been willing to pay?

We are not talking about getting rid of [SYMPTOM] forever: we are

talk ing about the amount of money you would have been willing to

pay to have eliminated the symptom that one time.

FURTHER EXPLANATION:

Think of this as the price of a special treatment that would

prevent the symptom one time. How high a price would you have

been willing to pay to eliminate the symptom this one time?

Q3h. What sum of money would you have been willing to pay?

19

6 0
Q4. OVERALL SYMPTOM VALUES

Now that I have a lot of information about the three individual symptoms, I

would like to ask a question that considers all three at once.

Let's add up the separate amounts you would pay to eliminate the severity of

all three Individual symptoms we talked about.

For [SYMPTOM 1] you said you would pay [WTP 1] and you said it happened

[ ] times per month. [WTP 1] x [-- TIMES PER MONTH] = ,

which is the amount you would pay to eliminate [SYMPTOM 1] on a monthly

basis.

For [SYMPTOM 2] you said you would pay [WTP 2] and you said It happened

[ ] times per month. [WTP 2] x [-- TIMES PER MONTH] =

which Is the amount you would pay to eliminate [SYMPTOM 2] on a monthly

basis.

For [SYMPTOM 3] you said you would pay [WTP 3] and you said it happened

[ ] times per month. [WTP 3] X [-- TIMES PER MONTH] =

which is the amount you would pay to eliminate [SYMPTOM 3] on a monthly

basis.

This gives a grand total of [AMOUNT 1] + [AMOUNT 2] + [AMOUNT 3] =

[SUM]

which is what you would be willing to pay to eliminate these three

symptoms. On a monthly basis Is [SUM] what you would be willing to pay to

eliminate these three symptoms?

(1) YES

(2) NO

38

20

6 1
IF NO:

Q4a. Would you be willing to pay more or less than [SUM].

(1) MORE

(2) LESS

Q4b. What dollar amount would you be willing to pay?

That is the last question.

As we said in the letter, we will be sending you a check for your help with our

study. Your check will be sent in the mail and will take about 4 - 5 weeks to

arrive. In order to print a check however, the University requires us to submit

your Social Security number along with your name and address. What Is your

Social Security number?

Social Security number

THANK YOU AGAIN FOR YOUR HELP.

21

6 2