Table 2.

Overview of the categories.

Main category	Subcategory	Questions
1. Delphi variants variants of Delphi technique	1.a Reporting quality	• How often did the investigated articles of the reviews contain a report of the Delphi variants?
	1.b Variants	• Which Delphi variants were used in the studies examined in the review?
2. Experts	2.a Reporting quality	• How often did the investigated articles of the reviews include a report on aspects related to the definition and selection of experts?
	2.b Number of experts	• How many experts were included in the Delphi technique? • How did the number of experts change over the different rounds?
	2.c Selection of experts	• Which categories of experts were included in the Delphi technique? • How were the experts identified and approached?
	2.d Expert panel	• How was the expert panel put together?
3. Consensus (Delphi studies that were explicitly designed as consensus methods were included here)	3.a Reporting quality	• How often did the articles contain a report about consensus aspects?
	3.b Definition and measurement of consensus	• How was consensus defined and measured? • What role did the stability of the answers play?
	3.c Consensus reached	• For how many items in the Delphi studies was consensus reached?
4. Delphi process	4.a Reporting quality	• How often did the investigated articles of the reviews contain a report of the specific process used?
	4.b Number of rounds	• How many rounds were used in the Delphi technique?
	4.c Questionnaire and scale development	• How were the questionnaires and the specific items for a Delphi technique developed?
	4.d Response rate	• How high was the response rate from the experts both when initially approached and also for the individual rounds?
	4.e Feedback design	• How was the feedback designed?