gms | German Medical Science

Background and status of (inter)national research: Recruitment is one of the main issues in any research that depends on participant involvement. Previous studies show varying results of the use of a color photograph of the researcher to postal questionnaires. (1, 2)

Question and objective: This study within a trial (SWAT) aims to assess whether invitation letters including researcher photographs increase the recruitment rate in the context of a survey on medical second opinions.

Method or hypothesis: We registered our SWAT at Queens University Belfast (SWAT 104). Through 25 local register offices, we identified a random sample of 9,990 persons. For selection of participants, we used 1:1:1 disproportionate stratified sampling with settlement pattern (urban area, area with agglomeration, rural area) as the stratification variable. We randomly assigned our sample to the intervention group (IG) and control group (CG) in a 1:1 ratio. The IG received an invitation letter with a photograph of both researchers, and the CG received an invitation letter without photograph. We had originally planned to split each group further into two subgroups, one receiving the material in an envelope with a printed teaser, the other in a blank envelope. Unfortunately, all envelopes were sent out as blank envelopes, so that we did not follow up on this additional intervention. The questionnaire comprised 14 pages and 47 items. Participants could opt to take part in a lottery and win an Amazon coupon (125x50€). We contacted our sample twice via post. Our primary outcome was the response rate in each group. We performed subgroup analyses for gender and settlement pattern (urban area, area with agglomeration, rural area).

Results: From 9,990 persons contacted, 193 invitations were returned as undeliverable and were excluded. We received 1,341 responses to our survey. There were 679/4,890 (13.9%) responses in the IG and 662/4,907 (13.5%) in the CG with an odds ratio of 1.03 (95% confidence interval: 0.94; 1.16). Subgroup analyses did not reveal any differences. Neither gender nor settlement pattern seem to have any impact on the response rate.

Discussion: The present results do not show any difference in the recruitment rates. In contrast to a previous study (showing an increase in the photography group), we did not rate the attractiveness of our photographs upfront. The greater length of our questionnaire compared to literature examples may have affected the results, as the general response rate was lower than stated in the literature.

Practical implications: There seems to be no difference in the response rate if people receive an invitation letter with a photography of the researcher or a letter without photography. Moreover their does not seem to be an impact of gender or settlement pattern. Other strategies, like the lottery, should be evaluated separately.

Appeal for practice (science and/or care) in one sentence: The influence of single strategies to enhance response rates should be evaluated comprehensively and with regard to the specific group.