Conclusion
In general, invitation letters with animation videos intended to increase response-motivation resulted in a similar or lower response proportion overall compared to a generic invitation letter without a video, hence no overall improvement in sample composition was reached. However, a positive effect on the response proportion was seen for the animation video targeted men aged 16–24 years compared to the generic invitation letter. Further, the three targeted animation videos tended to produce higher response proportions compared to the general non-targeted animation video. The heterogeneous findings suggest that there is potential for targeted animation videos to improve both response proportions and sample composition. The content of the video, the target group and timing of evaluation seem to be important for the use of targeted animation videos to be successful. This warrants further research to better identify in which contexts, in which subgroups and under which circumstances, animation videos are useful to increase response proportions.