Participants' experiences with the Delphi method: an online evaluation of a three-round Delphi across German-speaking countries.

Abstract

This study evaluates how participants experienced and assessed a three-round Delphi study on the terminology of developmental language disorders in childhood. It compares participants who completed all rounds (completers) with those who withdrew early (dropouts) and aims to derive methodological quality criteria for future Delphi studies. The evaluation is based on a Delphi study conducted in 2021/2022 across five German-speaking countries. After the final round, n=179 experts (40% response rate) completed a standardised survey assessing their expertise, motivation, reasons for discontinuation, time commitment and perceptions of questionnaire and feedback design. Responses from completers (n=156) and dropouts (n=23) were analysed descriptively. Most participants had no prior experience with Delphi methods but rated the study positively and considered the topic highly relevant. Completers reported their subjective time commitment to be lower and rated the handling of the questionnaire more positively than dropouts. Feedback was used by nearly half of all experts and was more actively considered by completers. Lack of time was the most common reason for discontinuation. The findings confirm the feasibility and acceptance of the Delphi method in interdisciplinary health research. In addition to established methodological principles, topic relevance, clear communication and time commitment emerged as key areas for expert motivation and engagement.