Supplementing CAPI with CATI in a nationally representative Health Survey – effect on non- response Michael Davidsen, Ola Ekholm Copenhagen, Denmark

Plan The Danish Health and Morbidity Programme Design of the 2005 survey Response rate and CATI supplement Interpretation problems Comparisons of groups Discussion and conclusion

The Danish Health and Morbidity Survey Programme Nationally representative health interview surveys of adult (age 16+) Danes Questions on health, symptoms, illness, ilness behaviour, life style, use of health care and much more ( General surveys conducted 1987, 1994, 2000 and 2005

The survey 2005 Based on a random sample from the Danish Civil Person Register Data collection from May – February (293 days) Initially only interview by CAPI SFI-SURVEY responsible for interviews

Invitation and interview Written invitation, letter of introduction Interviewer send letter and establish contact Interview in the home of the respondent Interviewer require more persons to interview.

Sample Strata defined by 5 Danish regions interviews with response rate 70% Two subsamples: 1. a re-re-interview of persons invited in 1994 and supplemented twice by young persons 2. a random sample ensuring adequate regional sizes

Demands Overall response rates: 70% Regional response rates: 70%, capital 64% 21,832 person invited 4,688 capital; 4,286 other regions

Response ratedevelopment

Rregional response rates December

CATI supplement Telephone contact to ’soft’ refuser, not met and out of town endorsed Only 3 regions Only by few ’super-interviewers’ January and February 2006 Same questionairre as with CAPI

CATI supplement Based on a pilot study of 40 persons with positive response rate. Information on ’soft refusers’ not available CATI response rate cannot be calculated Estimate based on pilot and information from SFI-SURVEY: 20%

Response rate final sample

Result of CATI supplement

Reginal response rate in sample

Distribution according to interview status

Effect of interview mode on selected health indicators

Discussion and conclusion I CATI supplement designed to improve response rate Reasonable success late in data collection Some conflicting interests when data collection company has interest in improving response rate

Discussion and conclusion II CATI seems to ’catch’ young, men and unmarried