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LONGER INTERVIEWS MAY NOT AFFECT 

SUBSEQUENT SURVEY PARTICIPATION PROPENSITY

PETER LYNN*

Abstract Survey researchers often assume that respondent burden is 

an important determinant of survey participation propensity and that 

interview length is a good indicator of burden. However, there is surprisingly little evidence of the effect of length of a completed interview on 

subsequent participation propensity, particularly in the case of face-toface surveys. This article presents results from a large-scale randomized 

experiment in which respondents experienced interviews of different 

lengths at wave 1 of a panel survey. Subsequently, respondents were 

asked to complete a self-completion questionnaire and then to take part 

in further waves of the survey. For each of these subsequent tasks, the 

study compares completion rates between those administered the shorter 

and those administered the longer version of the wave 1 interview. No 

evidence is found that wave 1 interview length affects subsequent participation propensity.

Introduction

Survey designers must decide how much content should be included in a 

questionnaire. There is often pressure to include additional questions, as this 

can widen the analytical potential of a survey data set for a relatively modest 

cost. But additional questions can also have negative implications. The additional time that it consequently takes a respondent to complete the interview 

or questionnaire may impose greater cognitive burden, greater discomfort, or 

greater disruption to their other activities. These difficulties are characterized 

by survey researchers as components of respondent burden (Bradburn 1978; 

Peter Lynn is a professor of survey methodology at the Institute for Social and Economic 

Research, University of Essex, Colchester, UK. This study was funded by an Economic and Social 

Research Council Award [ES/H029745/1, “Understanding Society and the UK Longitudinal 

Studies Centre,” to Nick Buck]. Important contributions to the design, management, and data 

preparation of the waves of the Innovation Panel used in this study were made by Noah Uhrig, 

Jon Burton, Alita Nandi, Gundi Knies, and other ISER colleagues. Data collection was carried out 

by NatCen Social Research. *Address correspondence to Peter Lynn, ISER, University of Essex, 

Wivenhoe Park, Colchester, Essex CO4 3SQ, UK; e-mail: plynn@essex.ac.uk.

Public Opinion Quarterly, Vol. 78, No. 2, Summer 2014, pp. 500–509

doi:10.1093/poq/nfu015 Advance Access publication July 22, 2014
Sharp and Frankel 1983), a phenomenon that may affect the quality of answers 

given to survey questions, particularly later in an interview (Krosnick 1999; 

Holbrook, Green, and Krosnick 2003; Galesic 2006; Roberts et al. 2010), and 

may affect the willingness of the respondent to undertake subsequent additional survey tasks. The latter consideration is particularly pertinent in the case 

of longitudinal surveys, where value comes from having the same respondents 

participate repeatedly. Thus, to help survey designers make decisions about 

instrument length, this study presents evidence of the effect of additional 

content on respondent propensity to agree to participate in subsequent survey 

tasks. Data come from a large-scale randomized experiment with a nationally 

representative sample in which respondents experienced interview instruments 

of different lengths at wave 1 of a panel survey. The study presents estimates 

of the effect of interview length on completion rates of a self-completion questionnaire administered immediately after the interview and on requests for 

subsequent interviews at one-year intervals.

Background

As a concept, questionnaire/interview length is broad and has been defined 

and operationalized in different ways by different researchers.

In the context of studying the effect of questionnaire length on participation 

propensity in mail surveys, researchers have tended to focus on the number 

of questionnaire pages or, less frequently, the number of items (Yammarino, 

Skinner, and Childers 1991; Dillman, Sinclair, and Clark 1993; Dillman, 

Smyth, and Christian 2008). This approach makes sense, as in the mail survey 

context the entire questionnaire is visible to the sample member before he or 

she decides whether or not to complete it. It is likely that a sample member 

will form an idea of the amount of effort required to complete the questionnaire based on a cursory impression of the number of pages and questions. 

Longer questionnaires have generally been found to reduce response rates on 

mail surveys (Heberlein and Baumgartner 1978; Yammarino, Skinner, and 

Childers 1991; Dillman, Smyth, and Christian 2008), though Champion and 

Sear (1969) found that, holding the number of items constant, a three-page 

questionnaire obtained a lower response rate than either six-page or nine-page 

versions.

In other survey modes, sample members are unable to form their own 

impression of the amount of effort required to participate, but instead rely 

on information communicated by the researcher. The communication may be 

written (a prenotification letter, an invitation to participate in a web survey) 

or verbal (via an interviewer). Studies of the effect of length on participation propensity have therefore tended to focus on the statement made by the 

researcher/ interviewer about the anticipated time required to participate (e.g., 

Collins et al. 1988; Groves et al. 1999; Crawford, Couper, and Lamias 2001; 

Interview Length and Subsequent Participation 501
Galesic and Bosnjak 2009). It has been found that increasing the time that 

respondents are told the survey will take reduces response rates both in web 

surveys (Crawford, Couper, and Lamias 2001; Marcus et al. 2007; Galesic and 

Bosnjak 2009) and in telephone surveys (Collins et al. 1988; Roberts et al. 

2010). Groves et al. (1999) report a similar finding for face-to-face surveys, 

though this is based on a laboratory study with low external validity.

Information provided to a sample member prior to starting the interview/

questionnaire is the only aspect of length that can affect an initial decision 

to participate. But this information is not necessarily a good predictor of the 

actual time that participation will require. Even if the researcher in good faith 

communicates an accurate mean interview length, the time that the interview 

will take for any individual respondent can vary substantially from the mean 

due to variation in circumstances, cognitive ability, response styles, and so on. 

Thus, the actual completion time, rather than the anticipated time, is likely 

to influence propensity to continue responding, and willingness to respond 

to additional requests. This is especially pertinent in the web survey context, 

where the study of breakoffs has paid attention to the role of elapsed time 

(Haraldsen 2002; Galesic 2006; Peytchev 2009). In interviewer-administered 

modes, breakoff is far less common and sample members who commence an 

interview usually complete it, regardless of the correspondence between anticipated and actual completion time. Furthermore, it has been argued that the 

respondent’s perception of completion time may be more important than actual 

completion time (Bradburn 1978; Holbrook, Green, and Krosnick 2003), and 

that tolerance of longer interviews may be mode-dependent: Holbrook, Green, 

and Krosnick (2003) found that telephone respondents were more likely than 

face-to-face respondents to express dissatisfaction with the length of interview, even though their interviews were in fact shorter.

In the context of a longitudinal survey, or any other survey in which additional participation requests are made after the initial interview, there is 

scope for completion time to influence the respondent’s disposition to future 

requests. There have been only two prior experimental studies of this issue 

on interviewer-administered surveys. With face-to-face interviewing, Sharp 

and Frankel (1983) found no significant difference in wave 2 response rates 

between respondents administered a 25-minute interview and those administered a 75-minute interview at wave 1. With telephone interviewing, Fricker 

et al. (2012) found a lower wave 3 attrition rate among respondents administered a 21-minute wave 2 interview than among those administered a 29-minute interview. Almost two decades ago, Bogen (1996) concluded that there is 

very little evidence of the effect of different-length instruments on subsequent 

survey participation. That state of affairs has hardly been altered.

Other studies have looked at the effect of variation in administration time of 

a single instrument. For example, Branden, Gritz, and Pergamit (1995) found 

that a longer interview was associated with less attrition in a telephone survey 

and concluded that this was likely due to greater salience of the questionnaire 

502 Lynn
content. But this addresses a different issue, the variation between respondents 

in the experience of the same instrument.

McCarthy, Beckler, and Qualey (2006) examined a different aspect of prior 

participation experience, namely the effect on subsequent participation of the 

number of previous survey requests received. They found that larger numbers 

of requests were associated with greater participation propensity, but their 

study was not based on an experimental design, so the association may not 

be causal.

Data

Data are from an experiment mounted on the UK Household Longitudinal 

Study Innovation Panel (UKHLS-IP). The UKHLS-IP is set up for the purpose 

of methodological development and testing (Uhrig 2011), primarily to service 

the main UKHLS, an academically led study designed to provide a multidisciplinary research resource (Buck and McFall 2012; Hobcraft and Sacker 

2012). The UKHLS involves annual interviews with around 70,000 adult sample members and all other adult members of their current household, while the 

UKHLS-IP is based on a much smaller sample—around 2,500 adults at wave 

1—but follows broadly the same design as the main survey.

The UKHLS-IP has a clustered, stratified, probability-sampling design 

(Lynn 2009). In summary, 120 postcode sectors were selected with probability proportional to size from a list of all sectors in Great Britain,1

 stratified 

by geographic region, socioeconomic classification, and population density. 

In each sector, an equal-probability sample of 23 residential addresses was 

selected. Each address was visited by an interviewer whose task was to identify all resident persons, all of whom became UKHLS-IP sample members. At 

wave 1 of the survey, all sample members aged 16 or over were eligible for an 

individual interview.

The experiment that forms the basis of the study reported here was incorporated into wave 1 of the UKHLS-IP, for which data collection took place 

from January to April 2008. Sample members were randomly assigned to two 

equal-sized groups, each of which were administered one of two versions of 

the individual interview, referred to hereafter as the “short interview” and the 

“long interview.” The short interview consisted of 26 modules of questions, 

administered face-to-face by a trained survey interviewer in the respondent’s 

home, using a CAPI instrument programmed in Blaise. Topics included demographics, family background, education, health and disability, employment 

and labor-market activity, job satisfaction, ethnicity, national identity, religion, 

and income. The long interview consisted of exactly the same instrument, but 

1. Excluding that part of Scotland that lies north of the Caledonian Canal, a remote area that 

accounts for approximately 0.1 percent of the population of Great Britain.

Interview Length and Subsequent Participation 503
with two additions. First, a module on partnership history was extended to 

include a complete lifetime fertility history. Second, an additional module of 

questions on attitudes to environmental issues was added.

Interview completion times were obtained from electronic time stamps 

incorporated into the CAPI script. Time was recorded at the start of the interview, at the start and end of each of the 27 modules of questions that constituted the interview, and at the end of the interview. In the analysis, total 

interview completion time is derived as the difference between the time at 

the end of the interview and the time at the start,2

 while completion time for a 

specific module is analogously derived as the difference between the times at 

the end and start of that module.

Mean interview completion time was 20 percent longer (P < 0.0005) with 

the long interview (31 minutes 3 seconds) than with the short interview 

(25 minutes 50 seconds), though there was considerable variation between 

respondents in interview length, partly reflecting the heavily routed nature 

of the questionnaire (figure 1). The additional interview time for the fertility 

and partnership history module was greater for women than for men (table 1), 

resulting in a significant difference between men and women in the time taken 

to complete the long-interview version of that section (mean 2 minutes 45 

seconds for men, 3 minutes 9 seconds for women, P = 0.03). There was no 

difference between men and women in the mean completion time for the environmental attitudes module (mean 2 minutes 4 seconds for men, 2 minutes 

10 seconds for women, P = 0.18). On average, women took 1 minute 25 seconds longer than men to complete the short interview (P = 0.04), but women 

took 3 minutes 12 seconds longer than men to complete the long interview 

(P < 0.0005).

Once an interview was completed, the interviewer requested the respondent 

to additionally complete a 22-item self-completion paper questionnaire with 

questions on the quantity and quality of sleep, mental health, neighborhood 

attachment, life satisfaction, attitudes toward risk, and friendship networks. 

The questionnaire was a 12-page booklet with instructions on the cover page, 

2. Among the 2,399 respondents, there were six for whom time-stamp data was unavailable and 

one for whom the time-stamp values were implausible. Analysis of interview completion time is 

restricted to the remaining 2,392 respondents. Edit checks for internal consistency and external 

validity were applied and resulted in total interview time being edited in 193 cases. These included 

96 cases for whom total interview time was missing and was replaced by the sum of the times 

for the 27 modules. For the other 97 cases, total interview time was implausibly long (over 2 

hours). For 48 of these cases, total interview time was replaced by the sum of the times for the 27 

modules. For the other 49, this would still have resulted in an implausibly long interview time. 

Inspection revealed that these were all cases with excessively long times for one or more of the last 

three modules. These modules asked, respectively, consent to linkage of administrative data to the 

survey responses, respondent’s contact details, and contact details for stable contacts. For these 49 

cases, the total interview time was reduced by the difference between the recorded time for these 

three modules and the mean time among other respondents for these three modules.

504 Lynn
nine pages of questions, and two blank pages. Where possible, the respondent handed the completed questionnaire back to the interviewer before he or 

she left the house (often, respondents would complete the questionnaire while 

the interviewer was interviewing another household member); in other cases, 

the questionnaire was collected on a later visit or mailed back to the survey 

organization.

Table 1. Completion Time for the Fertility History and Environmental 

Attitudes Modules, Means and Standard Deviations by Treatment 

Group and Gender

Long interview Short interview

Men Women Total Men Women Total

Fertility and partnership 

history – Mean 2:45 3:09 2:58 0:57 0:53 0:55

(Standard deviation) (2:34) (3:42) (3:15) (0:35) (0:37) (0:36)

Environmental 

attitudes – Mean 2:04 2:10 2:07 – – –

(Standard deviation) (1:08) (1:34) (1:23) – – –

N 544 645 1,189 534 669 1,203

Note.—All cell entries are minutes:seconds.

0

10

20

30

40

50

60

70

80

90

100

110

120

Interview completion time (minutes)

80 60 40 20 0 20 40 60 80

interviews

 short long

Figure 1. Distribution of Interview Length, for Short- and Long-Interview 

Treatment Groups.

Interview Length and Subsequent Participation 505
Wave 1 respondents were subsequently reapproached and asked to take part 

in further interviews at approximately one-year intervals. Wave 2 took place 

between April and June 2009, wave 3 between April and June 2010, wave 4 

between March and May 2011, and wave 5 between March and July 2012.

Results

Table  2 presents completion rates for each of the five subsequent survey 

requests that were made of the wave 1 respondents. No significant difference 

is observed in any of the completion rates between sample members administered the short interview at wave 1 and those administered the long interview. 

In all cases, the rates are remarkably similar. The same is true when the analysis is restricted to women, for whom the difference in wave 1 interview length 

was greater (table 3).

To test whether these results might depend on actual interview completion time, logistic regression analysis of each of the five completion rates 

was carried out, in which the independent variables were interview version 

(long or short), quartile of the interview length distribution,3 and the interaction between these two factors. None of the interaction terms were significant, 

indicating no significant effect of interview version on outcome for any of the 

quartiles (results not shown4).

Table 2. Outcome Rates for Subsequent Survey Requests, Full Sample

Outcome

Treatment

P

Short wave 1 

interview

Long wave 1 

interview

Self-completion 

questionnaire 90.0% (n = 1,205) 89.7% (n = 1,194) 0.78

Wave 2 interview 70.1% (n = 1,201) 70.5% (n = 1,187) 0.83

Wave 3 interview 63.0% (n = 1,190) 64.5% (n = 1,157) 0.46

Wave 4 interview 57.8% (n = 1,182) 57.0% (n = 1,147) 0.71

Wave 5 interview 49.9% (n = 1,171) 49.0% (n = 1,141) 0.67

Note.—The completion rate for each of the five survey tasks is conditional on participation at 

wave 1. The wave 1 response rate was 53.7 percent (AAPOR RR1). Additionally, for the wave 2 

to 5 interview rates, sample members known to have died prior to that wave, and therefore ineligible to be interviewed, have been excluded from the base. P-values are based on independent 

chi-square tests for each of the five survey requests.

3. To avoid endogeneity, for the purpose of this analysis interview length was defined as the time 

taken for all modules excluding the two modules in which the content differed between the two treatment groups. Thus, respondents are assigned to quartiles based on the time taken for identical content.

4. The results of this analysis are available in the supplementary materials online.

506 Lynn
Discussion

This study has found no effect of the length of the wave 1 survey instrument 

on subsequent participation propensity. This finding holds both for a request 

immediately following the interview (to complete a self-completion questionnaire) and for later requests to take part in interviews similar to the first 

interview. The finding also holds both for respondents whose wave 1 interview was relatively short (due to questionnaire routing) and for those whose 

interview was relatively long. The mean difference in length of the wave 1 

interview between the two instrument versions was modest, with the longer 

version being just over five minutes longer—a 20 percent increase in completion time. However, a difference of this magnitude represents a real decision that a survey designer may face. It is not unusual for survey designers 

to have to balance the analytical advantages of adding a few extra minutes of 

questioning against the perceived disadvantages of increasing the respondent 

burden by making the interview longer. The evidence presented here suggests 

that the disadvantage in terms of subsequent participation propensity may be 

negligible or nonexistent. This conclusion should be of particular interest to 

longitudinal survey managers.

It is reasonable to suppose that any effect of interview length might depend 

both on the absolute difference in completion time (five minutes in the present case) and on the relative difference (20 percent). Thus, we cannot rule 

out that a larger difference than the five minutes studied here could have an 

effect. Similarly, the finding of no effect for an absolute difference of five 

minutes might not hold if this corresponded to a larger relative difference; in 

other words, a shorter baseline completion time (though see Sharp and Frankel 

[1983]). As suggested by Hansen (2007), further experimental research could 

usefully shed light on this.

To put the findings of this study in context, it should be noted that increased 

respondent burden may have other effects. Though a participant may be willing 

to continue responding, the quality of provided responses could suffer when 

Table 3. Outcome Rates for Subsequent Survey Requests, Women

Outcome

Treatment

P

Short wave 1 

interview

Long wave 1 

interview

Self-completion 

questionnaire 90.8% (n = 671) 90.6% (n = 648) 0.91

Wave 2 interview 70.6% (n = 670) 70.5% (n = 647) 0.96

Wave 3 interview 63.2% (n = 663) 65.9% (n = 633) 0.31

Wave 4 interview 57.9% (n = 658) 57.7% (n = 627) 0.95

Wave 5 interview 50.0% (n = 654) 49.0% (n = 624) 0.73

Interview Length and Subsequent Participation 507
burden is increased (Sharp and Frankel 1983; Holbrook, Green, and Krosnick 

2003). Furthermore, we have no evidence on the relationship between interview completion time and perceived burden. It is plausible that the association 

is weak, with perceived burden being influenced at least as much by other factors, such as interest in the survey topic(s) and likeableness of the interviewer. 

In the case of this experiment, the additional questions in the long interview 

may have had a different level of salience to respondents, on average, than the 

questions in the rest of the interview.

Aside from potentially affecting respondent burden, increasing the interview 

completion time affects survey costs. Interviewers must be paid for longer 

hours, and a greater volume of data must be processed and managed. These 

factors should all be considered when deciding whether additional interview 

content is worthwhile.

Supplementary Data

Supplementary data are freely available online at http://poq.oxfordjournals.org/.

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