Table 3.

Measurements and classifications for each research question (see Table 1 for full descriptions)

No.	Short title	Measurement/classification scheme
RQ1	Most active researchers	No. of publications per unique researcher
RQ2	Author networks	Graphical analysis of co-authorships cycles
RQ3	Top venues	No. of publications per unique venue (i.e., conference/workshop series or journal)
RQ4	Papers per year	No. of publications per year
RQ5	Top cited publications	Graphical analysis of citation cycles, i.e., which papers on requirements engineering education are commonly cited by other papers on requirements engineering education
RQ6	Research methods	Classification according to Wieringa et al. [194], see Table 4
RQ7	Contributions	Classification according to Petersen et al. [140], see Table 5
RQ8	Keywords	No. of unique author keywords. Aggregated in case of different spellings, singular vs plural, etc.
RQ9	Learners	Audience of the proposed teaching intervention. Classification: university students (either undergraduate students, graduate students, or not further specified by the paper), industry professionals, school students, unknown
RQ10	Educational approaches and learning subjects	Categorization according to the paper author’s description