Background The involvement of older adults in research on digital health is uneven with respect to, for example, age, gender, health status, and digital skills. However, little is known regarding the effect of the uneven involvement of older adults in digital health research on researched outcomes. This study helps to fill this knowledge gap, identifies the effects of uneven involvement of older adults in digital health research on researched outcomes, and also develops a correction for this.Methods Data are retrieved from a digital health intervention for postoperative monitoring of people who underwent day surgery in Sweden. Based on field information on the recruitment process and researched outcomes for the intervention, this study (i) tested intervention effects by using 2 standard unweighted procedures in a sample of 281 individuals aged 50 years or older, and then (ii) used the information on participants, nonparticipants, and their respective probabilities to be involved in the intervention study to perform a weighting of the intervention effects for each step of selection and for the study group membership.Results The intervention effects were found to be overestimated due to overrepresentation of groups that gained from receiving the intervention. No intervention effects were found after adjustment for participation bias.Conclusions Selective participation of older adults in digital health research biases research outcomes and can lead to overestimation of intervention effects. Weighting allows researchers to correct and describe the effect of selective participation on researched outcomes.