Background. Most women in Germany have to decide whether they want to attend the Mammography Screening Programme to which they are invited once they turn 50. Informedness is an ethical requirement for decisions on screening but research shows that informed choice is not sufficiently realised. Decision aids are a promising class of interventions to realise informed choice as they improve knowledge, clarify values, and improve behavioural implementation of and satisfaction with a decision. However, there is a knowledge gap regarding which components of decision aids are effective. Manuscript 1 provides evidence for knowledge increase through use of crowd-figure-pictograms. Prior to this research project, no decision aid existed that aimed at average risk women in the target age group of mammography screening and was evaluated in a randomised controlled trial. Most previous studies on decision aids only looked at their immediate effect and did not follow-up on whether the decision was implemented and which medium-term effects the decision aid had on knowledge and post-decisional satisfaction. Therefore, a twofold gap remains: We lack (1) a decision aid appropriate for women invited to the German Mammography Screening Programme and (2) evidence on medium-term effects of decision aids.

Methods. The main research project of this dissertation developed a decision aid for women invited to the German Mammography Screening Programme for the first time and evaluated it in a randomised controlled trial with a 3-month follow-up. Acceptability and effectiveness of the decision aid including possible moderators (eHealth literacy and education) were evaluated. Details of the study protocol are presented in Manuscript 2. To be able to assess all relevant outcomes, two other research projects were employed for instrument development and validation. Development and validation of a questionnaire assessing informed choice are described in Manuscript 3; translation and validation of a measure for eHealth literacy are described in Manuscript 4.

Results. Women rated the decision aid as acceptable. Manuscript 5 provides evidence of the effectiveness of the decision aid: Women who had received the decision aid were more likely to make an informed choice, to have higher knowledge, and to have lower decisional conflict. Uptake was not affected. Manuscript 6 shows that the effect of the decision aid on knowledge was moderated by neither eHealth literacy nor education level.

Conclusions. This dissertation was the first to develop and systematically evaluate a decision aid for the German Mammography Screening Programme. To achieve this, it integrated the results of three related research projects for instrument development and testing of crowd-figure-pictograms. The developed decision aid was acceptable to its users and effective in increasing the proportion of informed choices. Knowledge was also increased through the decision aid irrespective of eHealth literacy or education level. Thus, the decision aid developed in this project is an important support tool for women deciding whether to participate in the Mammography Screening Programme.