Survey MethodologyNonresponse

EPID 626

Lecture 6

Lecture Overview

• Finish discussion of computer-assisted interview

• Discuss nonresponse

Computer assisted survey• More of a tool than a design really

– Can be used as a stand-alone self-administered survey

– Can be used in conjunction with telephone or personal interviews

– Can use in conjunction with video to simulate a personal interview

• If desired, you can match some characteristics, such as age, race, and gender of the interviewer with the subject (more on this later)

Computer assisted survey (2)

• Available information?– Depends on other elements of the study

design

• Survey population skills and motivation?– People who are not familiar with computers

may feel uncomfortable– Can adjust the language– Can read questions aloud

Computer assisted survey (3)

• Desired data? – Can follow complex question patterns or

questions tailored to previous answers– Can identify inconsistencies or missing

data before the interview is over– Can be useful in combination with

telephone survey

Computer assisted survey (3)

• Response rates? – Depends on other elements of the study

design

• Resources?– No data entry required– If it is self-administered, no interviewer

required

What is nonresponse?

• The failure to collect data from subjects selected to be in the sample

• Potentially one of the most important sources of systematic error in a study

• Unlike like random error, such as sampling error, nonresponse tends to bias estimates

3 categories of nonresponders

• Those whom the data collection procedures do not reach

• Those who refuse to provide data

• Those who are unable to provide data

Response rate

• Number of respondents X100%Number sampled

• Rule of thumb for minimum response rate is 75% (Fowler, 1993)

– adequate 50%– good 60%– very good 75% (Babbie, 1990)

Bias due to nonresponse

The bias is a function of:

• the response rate

• the extent to which nonresponders differ from the sample population

Generalizations

• Response rates are higher in rural areas than in urban areas

• Response rates are lower when there is a designated respondent than if you take any responsible adult

• Response rates are higher for topics that interest people

Why are response rates lower in urban areas?

• Higher proportion of single individuals

• More highrise dwellings (less accessible)

• Interviewers may be uncomfortable in urban areas at night

Do response rates differ by data collection method?

Mail surveys

• Those with an interest are more likely to respond

• Better educated people are more likely to respond

• This method generally has the lowest response rates, but with effort, response rates can be attained that are comparable to other methods

Phone and personal interview

• Availability bias-more likely to get housewives, unemployed, retirees, those with children, large households

Maximizing response rates in mail surveys

• Make the survey attractive and professional looking – use green paper

• Professional endorsement

• Prenotification

• Offer a monetary incentive

Maximizing response rates in mail surveys

• Make the survey quick and simple

• Include stamped, addressed return envelopes

• Mail reminders to nonresponders– usually every two weeks

• Follow-up nonresponders by telephone

Maximizing response in phone and personal interviews

• Vary call times, repeat unsuccessful calls

• Have flexible interview times

• Send informational letters ahead of time

• Communicate the survey purpose and importance to participant

• Use effective interviewers

Correcting for nonresponse

• Use proxy respondents

• Use statistical adjustments such as weighting subgroups to match their rate in the sample population

• Survey nonrespondents

Correcting for nonresponse(2)

• Wave analysis-compare those who responded in your first wave to those who responded only after follow-up– Assume that late responders are similar to

nonresponders

• Calculate the pattern of response in nonresponders needed to reverse the study conclusions

Survey nonrespondents

• Can survey with a pared-down instrument that contains only those variables that you expect to differ from sample population values or outcome variables of greatest interest

• In this case, stratify the calculation of sample estimate:

entsnonrespondn

srespondentn

xnnxnnx

n

r

nnrr

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