Table 2 Internal validity according to MMAT

Qualitative (n = 20)

S1. Are there clear research questions?

20

S2. Do the collected data allow to address the research questions?

20

1.1. Is the qualitative approach appropriate to answer the research question?

20

1.2. Are the qualitative data collection methods adequate to address the research question?

18

2

1.3. Are the findings adequately derived from the data?

17

3

1.4. Is the interpretation of results sufficiently substantiated by data?

18

2

1.5. Is there coherence between qualitative data sources, collection, analysis and interpretation?

20

Quantitative (n = 6)

S1. Are there clear research questions?

5

1

S2. Do the collected data allow to address the research questions?

5

1

4.1. Is the sampling strategy relevant to address the research question?

4

2

4.2. Is the sample representative of the target population?

5

1

4.3. Are the measurements appropriate?

6

4.4. Is the risk of nonresponse bias low?

2

1

3

4.5. Is the statistical analysis appropriate to answer the research question?

5

1

Mixed methods (n = 3)

S1. Are there clear research questions?

2

S2. Do the collected data allow to address the research questions?

2

5.1. Is there an adequate rationale for using a mixed methods design to address the research question?

2

1

5.2. Are the different components of the study effectively integrated to answer the research question?

2

1

5.3. Are the outputs of the integration of qualitative and quantitative components adequately interpreted?

2

1

5.4. Are divergences and inconsistencies between quantitative and qualitative results adequately addressed?

1

2

5.5. Do the different components of the study adhere to the quality criteria of each tradition of the methods involved?

1

1

1