THE USE OF SIMPLE INDICATORS FOR DETECTING POTENTIAL
CORONARY HEART DISEASE SUSCEPTIBILITY IN THE AIR TRAFFIC
CONTROLLER POPULATION

I. Introduction.

According to the most recent epidemiological
statistics, diseases of the cardiovascular system
caused 54.1% of all deaths in the United States."
Arteriosclerotic heart disease (including coronary
heart disease) caused 31.0% of all deaths in the
United States. In a 1960-1962 national survey
of heart disease prevalence, coronary heart disease
(CHD) was found in 5.0% of all adults in the
age range of 18-79 years Furthermore, the
presence of silent CHD in the general population
is amply documented by clinical?* as well as
postmortem studies.“* There is also ample
documentation of a surprising amount of early
silent CHD in people under 30 years of age.”!?
According to a recent estimate,!* silent CHD is
present in a minimum of 5.0% of United States
males over 35 years of age. <A recent study
has reviewed the manifold positive evidences re-
lating silent CHD to sudden incapacitation and/
or sudden death. Based on the first 14 of 20 years
experience, the Framingham Heart Study (FHS)
has reported that 57.8% of the 102 male and
38.9% of the 18 female CHD deaths observed
were sudden in nature.** In this same study,
sudden CHD death was defined as “sudden and
unexpected collapse and death within one hour
(but ordinarily in a matter of minutes) in ap-
parently well persons.” In view of the unex-
pectedness of 65.0% of these 120 CHD deaths,
and the absence of a prior definite CHD diag-
nosis in 62.8% of the 78 unexpected deaths, this
study ** strongly concluded that “the only road
to a substantial reduction in premature CHD
mortality is the prevention of CHD.” Despite
the prior absence of a definite CHD diagnosis,
80% of the victims of sudden, unexpected CHD
death had previously manifested CHD suscep-
tibility in one or more of the FHS coronary
profile parameters.’>

In a recent congressional hearing, the Federal
Air Surgeon reemphasized the role of medical
vigilance in the detection of silent or overt forms
of CHD in the airman population with especial
concern regarding the facet of sudden and un-
predictable incapacitation.“* One basis for this
continued concern is the fact that, in the 1963-
1970 period, 52.0% of the reconsidered actions by
the Federal Air Surgeon were directly related to
cardiovascular pathology.”

As of December 31, 1970, the active airman
population consisted of approximately 727,000
persons.7 Taking into account the biennial ex-
amination of third class airmen, the FAA con-
ducted the medical certification examination of
444,000 airmen in 1970. It appears reasonable
to assume that the repetitively examined airman
population may have less silent CHD than the
general population and that a maximum estimate
for this particular condition in the airman popu-
lation would be less than 5.0%.'* One possible
way of detecting this maximum 5.0% aliquot
would be the comprehensive cardiological exami-
nation of the 444,000 airmen in one year. One
hundred dollars would appear to be a conservative
cost estimate for a comprehensive cardiological
examination. Although strong in diagnostic
certainty, this solution for detecting the maxi-
mum 5.0% CHD aliquot, at a cost of approxi-
mately 44.4 million dollars per year, would be
economically inefficient. Other solutions have
been and continue to be sought. This report
presents and explores one such possible solution
in the specific context of the air traffic con-
troller (ATC) segment of the airman population.
A similar report focused on the third class air-
men is currently in preparation.

In a previous report,"® an analysis was made of
an eight-year interval change in several FHS
indicators of CHD susceptibility as measured on



than weaken any conclusions reached in this
study.

Since resting BP and HX, date of birth, height
and weight data are easily obtainable and are, in
fact, already included in th» standard aeromedical
certification examination, no additional expendi-
ture of time or money is nvolved in their com-
bined use as an adjunct screening aid for the
detection of CHD. The eurlier mentioned alter-
native of a comprehensive 2ardiological examina-
tion each year for every A’CC personnel is hardly
economical or desirable.

The screening identifica ion of any ATC per-
sonnel manifesting a high clegree of relative CHD
susceptibility provides a: important starting
point for a comprehensive attack on all phases of
CHD with the eventual goal of its elimination
from this population segment. Initially, the
identification of these individuals focuses the most
logical site for a sharply defined application of
comprehensive cardiological examination. The
identification of the highly susceptible individual
with or without accompaaying covert CHD is
especially important in v:ew of the potentially
grave aviation effects of suden and unpredictable
incapacitation ** and in v ew of the definititive
reports that these two types of incapacitation due
to CHD are usually prececed by major abnormal

displacements of FHS susceptibility parameters’*
and/or covert CHD." It is a policy of the Fed-
eral Aviation Administration that controllers who
do not successfully pass required physicals are not
permitted to man operational positions. The
identification of high susceptibility and/or covert
CHD individuals would afford the option of
pursuing remedial rehabilitation regimens. In-
dividuals possessing real but moderate to minor
degrees of susceptibility could optionally engage
in remedial programs aimed at partial and/or
complete reduction of the susceptibility. Those
individuals manifesting normality in all CHD
susceptibility indicators could optionally be en-
couraged through educational channels to engage
in preventive maintenance regimens of several
varieties. In this latter category, the earliest de-
tection of minor departures from optimum
cardiovascular health could be countered swiftly
and most efficiently for return to complete cardio-
vascular normality. A concerted effort of this
type at all of these levels could eventually reduce
CHD in the ATC population to the barest mini-
mum and hence achieve the fullest meaning for
the cardiovascular aspect of the ATC health
maintenance program. The degree to which such
efforts succeed should be reflected in enhanced
aviation safety.


spectively. In the All FRWIs and All Ages
columns of both tables an increase in both SBP
and DBP with increasing age and obesity are
quite apparent. That age and obesity may be
acting independently on the SBP and DBP is
strongly suggested by the same pattern of in-
crease within each of the age and FRWI
segments. The summary tables of nine major
population samplings of age versus blood pres-
sure were examined in relevance to the All
FRWIs data columns of Tables 1 and 2. Com-
pared across age groups alone, the SBP and
DBP values in Tables 1 and 2 were greater than
those in two of these studies ** and less than those
in the remaining seven.??*4?5 In one of these
studies ** based on data from 235,000 males, a
single-table summary of age versus height and
weight categories for resting SBP and DBP was
compiled. Mathematical conversion of these
height and weight data to FRWI equivalents for
a subsequent comparison with equivalent age and
FRWI categories in Tables 1 and 2 was accom-
plished. Compared on this basis, all SBP and
DBP values in Tables 1 and 2 were greater than

Taste. 1. Tabulation of Mean SBP Versus Age and
FRWI Categories. Each table cell contains the mean
SBP value (in mm Hg), the standard error of the
mean (+ mm Hg) and in parentheses, the number of
data used in their calculation.

AGE (yrs.)
FRWI
(%)

<30 30-39 | 40-49 > 50 | All Ages
120.7 | 121.1 123.7 127.8 121.8
<100.0 |} £0.14 | £0.16 | +0.27 | 40.46 £0.11
(5487)| (4935), (2086) (809)|(18, 817)
125.1 125.4 128.2 131.0 126.3
100.0— || £0.19 | 40.18 | 40.28 | 40.55 +£0.11
119.9 (2861)| (4009); (1927) (760)| (9, 557)
122.2 123.0 125.9 129.3 123.7
<120.0 || 40.08 | £0.12 | 40.19 | £0.35 +£0.07
(8348)| (8944)| (4013)| (1589) )(22, 874)
130.9 | 181.3 | 183.1 136.2 131.9
2120.0 || £0.61 | £0.55 | +1.11 | £1.81 +£0.39
(294) (400) (194) (64) (952)
122.5 123.4 126.2 129.6 124.0
All +0.12 | +0.12 | 40.20 | £0.33 +£0.08
FRWIs (8642); (9344)| (4207)} (1633)|(23, 826)

Tapre 2. Tabulation of Mean DBP Versus Age and
FRWI Categories, Hach table cell contains the mean
DBP (in mm Hg), the standard error of the mean
( mm Hg) and in parentheses the number of data
used in their calculation.

AGE (yrs.)
FRWI
(%)

<30 30-39 | 40-49 > 50 | All Ages

73.7 75.2 77.2 78.7 75.1

<100.0 || £0.11 | £0.12 | 40.18 | +£0.30 +£0.06
(5487)| (4935)) (2086) (809)} (18,317)

76.7 78.4 80.6 81.4 78.6

100,0— || £0.15 | £0.13 | 40.20 | +0.31 | +0.09
119.9 (2861); (4009)} (1927) (760)}. (9, 557)
74.7 76.6 78.9 80.0 76.5

<120.0 |} £0.09 | 40.08 | £0.13 | 40,22 £0.05
(8348)] (8944)) (4018)| (1589)) (22,874)

81.5 82.6 84.2 84.3 82.6

2120.0 || £0.46 | £0.41 | +0.66 | +1.08 +£0.28
(294), (400) (194) (64)} (952)

74.9 76.9 79.1 80.1 76.8

All +£0.09 | +0.09 | 40,12 | 40.21 | +40.04
FRWIs (8642)) (9344)| (4207)) (1633)|(23, 826)

those of the compared population study.** Per
se, none of the SBP and DBP values in Tables
1 and 2 are considered to be medically
abnormal,” 25 The points of salient interest in
Tables 1 and 2 are the increase in SBP and DBP
with both age and obesity, and the concentration
of the higher blood pressure values in the com-
bined older/obese categories.

Table 3 presents the age versus FRWI tabula-
tion of mean resting HR values. Per se, none of
the HR values in this table are considered to be
medically abnormal.*t In the All Ages and All
FRWIs columns, an increase in HR with increas-
ing age and obesity is apparent, although the
increments of HR increase in the latter column
are appreciably small. With few exceptions a
pattern of HR increase within each segmental
age and FRWI category is present, again sug-
gesting the possibility that age and obesity may
be acting independently on the resting HR.

Table 4 presents the age versus FRWI tabula-
tion of the 400 pathology code % prevalence.
The parenthesized value in each table cell repre-
sents the % prevalence of the 400 pathology code.



475 male ATC personnel. The initial measure-
ments were obtained from these personnel as ATC
students in 1960-1963 and the subsequent data
were obtained eight years later from their cur-
rent aeromedical certification records. The dis-
tribution of each of the parameters used was
compiled in an age versus Framingham relative
weight index (FRWI) table. The FRWI was
used as a measure of obesity. In accordance
with the FHS, frank obesity was defined as a
minimum FRWI of 120.0%.° The distributions
of the 1960-1963 data revealed a general trend
of parametric increase with age and FRWI.
This is consistent with the FHS report of rela-
tively greater CHD susceptibility with increased
age and obesity.” The distributions of the eight-
year interval data revealed the same general trend
of increase with age and FRWI. Moreover, an
additional shift in the distributions of all the
parameters occurred which resulted in an in-
creased concentration in the older/obese cate-
gories. This shift was interpreted as a trend of
advancing relative CHD susceptibility over the
eight-year period. On the assumption that the
FHS findings are generally correct, one logical
initial focus for comprehensive cardiological ex-
amination for CHD should be the oldest/most
obese individuals in whom the adjunct FHS
parameters were most indicative of the highest
relative CHD susceptibility. This approach
could become a quite useful adjunct for initial
CHD screening of large segments of the airman
population * at no additional expense to the
FAA. One such segment is comprised of ap-
proximately 23,000 ATC personnel. In order to
seek corroboration of the earlier findings** in
support of the initial CHD screening possibility,
an analysis of similar data from 23,826 male ATC
personnel was undertaken.

Il. Methods.

A. 1971 Data. All data were obtained from
the active aeromedical certification records in
January 1971. Age was expressed as the nearest
completed year on the day of the aeromedical
certification examination. Height (in inches) and
weight (in pounds) are stated rather than meas-
ured data. Both of these parameters are vulner-
able to errors of stated-type data. Where dis-
covered and confirmed, height errors were
corrected, Regarding stated weight, two com-

prehensive studies 2° 2? have reported that heavy
men tend to underestimate their weights while
light ones tend to overestimate theirs. In this
report, the uncorrected stated weights were used
as the best available data. The effect of possible
errors in stated height and weight on the screen-
ing value of the FRWI will be treated in the
discussion séction of this report. A separate re-
port concerning height and weight errors in
aeromedical certification data is currently in
preparation.

The resting systolic and diastolic blood pres-
sures (SBP and DBP) were measured using
standard medical procedures as prescribed in the
FAA Guide for Aviation Medical Examiners. In
accordance with this same Guide, the resting
heart rate (HR) is determined with the in-
dividual relaxed in a sitting position.

The 1965 revised pathology codes of the avia-
tion medical service list all cardiovascular
pathology under the 400 series. Once documented
and coded, critical items in this series are perma-
nently retained in the individual’s medical cer-
tification file. Non-critical items may be found
in the individual’s current file, only if they are
currently present. In this analysis, no distinction
was made between critical and non-critical code
items. However, it appears reasonable to assume
that the presence of any 400 series item would
generally confer a greater relative cardiovascular
susceptibility than its absence.

B. Age Versus FRWI Tables. The general
rationale of this table format has been presented
in a previous report.* The FHS rationale and
formula for the calculation of the FRWI have
been reported previously.*? The commensurate
regression formula, as estimated from the male
height and weight data of the 1960-1962 National
Health Survey, was virtually identical.* An
FRWI of 100.0% indicates that the weight of
the individual is equal to the median weight of
the FHS males of his identical height at the 1950
inception of the FHS.27 An FRWI of 120.0%
or greater indicates frank obesity. For the
purposes of this analysis, five categories each of
FRWI and age were used in each age versus
FRWI table.

III. Results.

Tables 1 and 2 present the age versus FRWI
tabulations of mean SBP and mean DBP re-


myocardial infarction and sudden death was
distinctly and impressively related to the ante-
cedent level of both systolic and diastolic blood
pressure. Risk was related not solely to ‘hyper-
tension’ but was proportional to the level of
blood pressure—even at non-hypertensive pres-
sures—from the lowest to the highest recorded.”
Therefore, if covert CHD is present at all in the
ATC population, it appears reasonable to assume
that comprehensive cardiological examination
would most probably reveal a greater % preva-
lence of the CHD in the older/obese combined
categories with the higher blood pressures than in
the younger/thinner combined categories with
the lower blood pressures.

A detailed rationale for the relationship be-
tween increased resting HR and CHD suscep-
tibility has been presented in a previous report.!®
Although none of the HR values in Table 3 are
considered to be medically abnormal,’ a general
pattern of increase with age and obesity is pres-
ent. The increase in HR with age within each
FRWI segment appears to be much smaller than
the increase in HR with FRWI within each age
segment. In the greater than 50 years column,
the HR of the 120.0% or greater FRWI group
departs from the trend of increase seen in each
of the other segmental age groups. This de-
parture from the general pattern of increase
might possibly be ascribed to some measurement
artifact or possibly reflect the already accom-
plished departure from this specific group of
overt CHD victims having higher resting HRs.
At present, the settlement of this point is moot.
However, the general pattern still supports an
increasing relative CHD susceptibility with age
and obesity and a logical primary focus on the
older/obese combined categories for intensified
CHD screenings.

Because of the unequivocal documented nature
of 400 pathology code incidents, the data in Table
4. constitute the strongest evidence in support of
the presence of an increasing relative CHD
susceptibility with age and obesity and the con-
centration of the highest relative susceptibility
in the older/obese combined categories. The gen-
eral patterns of increase in BP and HR with age
and obesity parallel the 400 pathology code data.
Since the highest % prevalences of the 400
pathology code are concentrated in the older/
obese combined categories and since the FHS has
shown a definite increased CHD susceptibility

and incidence in older and obese males,? * it seems
reasonable to hypothesize that the concomitant
presence of advanced age, frank obesity (120.0%
or greater FRWI) and relatively elevated BP
and HR values may reflect a substantial displace-
ment from cardiovascular normality. In any
event, it would appear relatively easy to test the
hypothesis that more covert CHD exists in the
older/obese combined categories with relatively
elevated BPs and HRs than in the younger/
thinner combined categories with relatively lower
BPs and HRs. A test of this hypothesis would
consist simply of comprehensive cardiological
examination of representative aliquots from these
two polar categories at approximately the same
point in time.

The detailed rationale for using the age versus
FRWI tables of SBP, DBP and HR as an
adjunct aid to mass aeromedical screening for
detection of covert CHD was presented in the
introduction section of this report. Although the
combined use of these parameters alone will not
detect the presence of covert CHD in a medically
unequivocal manner, in complete accord with the
FHS findings and the present 400 pathology code
data, they are capable of delineating those per-
sons within this population having the highest
relative potential for this disease. In the interest
of the most efficient, economical manner of detect-
ing covert CHD within the ATC or any other
population segment, it appears reasonable to
focus comprehensive cardiological examinations
initially on those personnel manifesting the
highest. relative susceptibility to this disease.
The paramount virtue of the parametric battery
described here as a delineator of relative CHD
susceptibility lies in the simplicity of the
parametric measurements per se. Resting BP
and HR are readily measured with acceptable
accuracy. Age, as measured from date of birth,
is relatively immune to error. Height and
weight, from which the FRWI is calculated, are
stated rather than measured data. When stated,
both of these parameters are subject to some de-
grees of error. A detailed report covering
height and weight errors in aeromedical certifica-
tion data is currently in preparation. In the
present study, all detected height errors were
corrected whereas the stated weights were ac-
cepted as the best available data. The directional
influences of errors in both of these parameters
are such that corrections would strengthen rather



TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. D. Gow ment Accession Now B. Recipient's Catalog No.
FAA-AM-72-20

@_ Title ond Subtitle 5. Repo Date

THE USE OF SIMPLE INDICATORS FOR DETECTING POTENTIAL May 1972

CORONARY HEART DISEASE SUSCEPTIBILITY IN THE AIR 6. Performing Organization Code

TRAFFIC CONTROLLER POPULATION

7. Authors) 3. Performing Organization Report No,

Michael T. Lategola, Ph.D.

9. Performing Organization Name and Address 10. Work Unit No.
FAA Civil Aeromedical Institute
P. O. Box 25082 TT. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name ond Address

Office of Aviation Medicine OAM Report
Federal Aviation Administration
800 Independence Avenue, S.W. 14. Sponsoring Agency Code

Washington, D. C. 20591

15. Supplementary Notes

Work was performed under Tasks AM-D-67-PHY-1 and AM-B-71-PHY-2.

16. Abstract

In report number FAA-AM-71-19, an analysis was made of an eight-year interval

change in several indicators of coronary heart disease (CHD) susceptibility as
measured on 475 male air traffic control (ATC) personnel. The initial measurements
were obtained from these personnel as ATC students in 1960-1963 and the subsequent
data were obtained eight years later from their current aeromedical certification
records. This analysis revealed a general trend of advancing relative susceptibili-
ty to CHD with age and obesity. Sample sizes (in age by obesity cells) were
frequently too small to warrant any statement of significance for this general trend,]

As a logical followup, an analysis of similar data from 23,826 male ATC personnel
was accomplished. The data were obtained from current aeromedical certification
records in January 1971. The distributions of resting blood pressure (BP), resting
heart rate (HR) and the 400 pathology code frequency were compiled in age versus
Framingham relative weight index (FRWI) tables. Obesity was defined as a minimum
FRWL of 120.0%. Substantiating earlier findings, all parameters generally increased
with age and obesity. These findings are directly relevant to the mass aeromedical
screening, early detection, susceptibility reversal and preventive aspects of CHD.

17. KeyWords ATC personnel, Cardiovascular | 18. Distribution Stotement ;
health, Coronary heart disease, Aero- Availability is unlimited. Document may

medical screening, Age, Obesity, Blood be released to the National Technical .
pressure, Heart rate, Cardiovascular Information Service, Springfield, Virginia
: 22151, for sale to the public,

pathology
19. Security Classif. (of this report) 20. Security Classif. (of this page) 2. No, of Pages | 22. Price
Unclassified Unclassified 7 $3.00

Form DOT F 1700.7 (s-69)





1

N

s

a

=

2

10.

11.

12.

18.

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Statistical Abstract of the United States, 91st Edition,
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Stokes, J. and T. R. Dawber: The “Silent Coronary”:
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Price, L.: Severity of Myocardial Infarction in Gar-
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Achor, R. W. P., W. D. Futch, H. B. Burchell and
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Johnson, W. J., R. W. P. Achor, H. B. Burchell and
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Gould, S. E, and L, P. Cawley: Unsuspected Healed
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Averial, K. H. and L. EB, Lamb: Electrocardiographic
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Smith, G. B, and L, E, Lamb: Electrocardiographic
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Anderson, J. R.: Case Report of Death Due to
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Master, A. M. and A. J. Geller: The Extent of Com-

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Aeromedical Certification Statistical Handbook, Fed-
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‘Taste 8, Tabulation of Mean Resting HR Versus Age
and FRWI Categories. Each table cell contains the
mean resting HR (in beats per minute), the standard
error of the mean (+ beats per minute) and in pa-
rentheses, the number of data used in their calculation.

AGE (yrs.)
FRWI
(%)
<30 | 30-39 | 40-49 | >50 | All Ages
73.7) 73.9] 74.2| 74.4 73.9
<100.0 |} £0.12 | 40.12 | £0.18 | 40.30 | 40.07
(5487)| (4935); (2086)|  (809)}(13, 317)
74.3) 74.5| 74.7 | 75.0 74.5
100.0— || £0.15 | 40.13 | £0.19 | £0.20 | +0.08
119.9 (2861)| (4009)| (1927)}  (760)| (9, 557)
73.9| 74.2) 74.5} 74.6 TA
<120.0 || 40.09 | +0.08 | £0.14] £0.21 | +0.05
(8348)} (8944)}  (4013)| (1589)|(22, 874)
76.7) 76.8| 76.6| 74.2 76.5
2120.0 | 40.54 | +0.44,) £0.66 | 40.42 | 40.20
(294)|  (400)| (194)}—(64)}—-(952)
74.0| 74.3) 74.5] 74.6 TA.
All +£0.09 | £0.08} £0.13 | £0.21 | 40.05
FRWIs || (8642)} (9344)| (4207)| (1633)|(23, 826)

In the All Ages and All FRWIs columns of this
table an increase in 400 pathology code %
prevalence with increasing age and obesity is
clearly manifested. That obesity and age may
be acting independently on the 400 pathology
code % prevalence is strongly suggested by the
same pattern of increase within each age and
FRWI segment. The increased concentration of
this parameter in the combined older/obese cate-
gories is of primary interest.

IV. Discussion.

In general corroboration of the findings pre-
sented in a previous report,'* the trends of the
parameters presented here in similar age versus
FRWI tables support the presence of a relatively
increasing CHD susceptibility with age and
obesity in the entire ATC population. Further,
a general concentration of the most elevated
parametric values reflecting the highest relative
susceptibility to CHD occurs in the combined
older/obese categories.

Although all the SBP and DBP values in
Tables 1 and 2 appear to be well below the
threshold values for marked CHD susceptibility,
a general increase with age and obesity is ap-
parent with a concentration of the higher values
in the combined older/obese categories. Although
the highest SBP and DBP values in the combined
older/obese categories do not exceed the threshold
values for marked CHD susceptibility,** it ap-
pears quite reasonable to assume that a greater
relative CHD susceptibility exists in these cate-
gories than in the younger/thinner counterpart
categories manifesting the lower SBP and DBP
values. Over its 20 years of experience, the FHS
has definitely established the prospective relation-
ship of initial hypertensive levels of blood
pressure (>160 mm Hg SBP and/or >95 mm
Hg DBP) to the subsequent development of
overt CHD.%*7?8 This relationship is a con-
tinuum which includes non-hypertensive levels of
blood pressure.*® As specifically stated in this
particuar FHS report ** based on the first 14 of
its 20 years of data: “Risk of every manifestation
of CHD including angina, coronary insufficiency,

Taste 4, Tabulation of the 400 Pathology Code %
Prevalence Versus Age and FRWI Categories. Each
table cell contains the ratio of the 400 code prevalence
number to the total number of cell individuals and in
parentheses, the equivalent of the ratio in terms of
% prevalence.

AGE (yrs.)
FRWI
(%)

<30 30-39 | 40-49 > 50 | All Ages

73/ 102/ 108/ 88/ 371/

<100.0 | 5487 | 4935} 2086| 809 | 13,317
(1.8)}  (2.1)}  (5.2)| (10.9)} (2.8)
47] 122) } 141) | 101) | 41/

100.0— || 2861} 4009| 1927| 760 9557

119.9 (1.6)]  (8.0)) (7.8) (18.8)) (4.8)

120/ 224/ 249/ 189) 782/

<120.0 3284 8944 4013 1569 22,874
(1.4)| (2.5)] (6.2)] (12.0)} (8.4)
12) | 20/ 22/ 9/ 63/
= 120.0 294 400 194 64 952
(4.1)] (5.0)} (41.3)} (14.1)] (6.6)
All 132/| 244/ | 271; | 198/ | 846/
FRWIs || 8642 | 9344} 4207| 1633] 23, 82¢
(1.5)} (2.6)} (6.4)) (02.1)] (3.5)





ACKNOWLEDGMENTS

The author sincerely acknowledges the significant efforts of Mrs. Peg;
Lyne and Mrs. Paula Grape in several data processing areas. Mr. Charles
Booze and Dr. Earl Folk are gratefully acknowledged for their facilitation

of access to pertinent medical certification data and adjunct consultation
concerning data analysis.