Objectives The objective of screening programmes for cancer is to reduce mortality and morbidity of the concerned cancer disease. However, cancer screening programmes may also cause overdiagnosis, false-positive results, overtreatment as well as psychological or physical harms. National health agencies and cancer organizations prioritize a high screening participation rate in favour of a comprehensive, understandable and evidence-based informed choice. In pursuit of this goal, these organisers make use of different systematic influences: Use of relative risk reductions; Emission of harms/exaggeration of benefits; Pre-booked appointments; Explicit recommendation of participation; Inducing fear – often in combinations.

The objective of this study was to asses if the different categories of systematic influences had a significant effect on the intention to participate in a screening programme for a non-communicable life-threatening disease, when applied in an invitational folder, and whether the applied systematic influences are recognized by the participants.

Method We created seven different pamphlets, inviting the reader to a screening programme for a fictional non-communicable life-threatening disease. Five pamphlets encompassed one of the five abovementioned influences, one encompassed none, and one encompassed all five influences combined.

In different public places in Denmark, 600 random passer-by were randomised to one of the seven pamphlets. After reading the pamphlet participants were asked: 1) whether they intended to participate in the fictional screening programme, and 2) whether they were able to correctly identify the applied influences.

Statistical analysis (ײ) was used, to measure the effect the systematic influences had on intention to participate. A descriptive analysis of the participant’s ability to identify the influences was also conducted.

Results Ad 1) A statistically significantly (p<0.05) higher proportion intended to participate in the groups receiving pamphlets containing relative risk reductions (OR 2.09 (95% CI: 1.16 to 3.75)), omission of harms/exaggeration of benefits (OR 4.30 (95% CI: 2.38 to 7.77)) explicit recommendations (OR 1.83 (95% CI: 1.03 to 4.25)), fear appeals (OR 2.39 (95% CI: 1.35 to 4.25)), and all combined (OR 8.60 (95% CI: 4.43 to 16.69)). Ad 2). Only a minority of the participants were able to correctly identify systematic influences in the pamphlets, varying from 4.1% to 29.9%. Participants who correctly identified a systematic influence in a pamphlet had a decreased intention to participate compared to those who found the pamphlet informational or those who indicated the pamphlet was influencing their choice but failed to identify where.

Conclusions In this study, four of five categories of systematic influence proved to increase intention to participate statistically significantly, except for the category pre-booked appointments. The latter category also increased the intention to participate but not in a statistically significant manner. Only a minority were able to identify the systematic influences, and since not identifying an influence is associated with an increased tendency to intend to participate, our results suggests, that some participants intended to participate in the screening programme because they were not able to recognize that they were being influenced. This effect seems to increase with increasing potency of the influences.