Table 3.

Level of evidence for each study design

Research design*	Level of evidence	Abbreviation
Descriptive research
Systematic review of descriptive studies	1	Des-1
Prevalence study with analytical component	2	Des-2
Case series and prevalence study without analytical component	3	Des-3
Case report	4	Des-4
Experimental research
Systematic review/meta-analysis of experimental studies	1	Exp-1
Randomised controlled trial	2	Exp-2
Group quasi-experimental study (a.k.a. non-RCT)	3	Exp-3
Quasi-experimental study with single subject	4	Exp-4
Observational research
Systematic review/meta-analysis of observational studies	1	Obs-1
Cohort study	2	Obs-2
Case-control	3	Obs-3
Analytical cross-sectional study	4	Obs-4
Qualitative research
Systematic review/meta-synthesis of qualitative studies	1	Qual-1
Group qualitative studies with more rigour†	2	Qual-2
Group qualitative studies with less rigour	3	Qual-3
Qualitative study with a single informant	4	Qual-4

1=Highest level of evidence; 4=lowest level of evidence.

*The following terminology of Tomlin and Borgetto’s model has been modified to align with the included research designs in this study: association/correlation studies=prevalence studies with analytical component; normative/descriptive studies=prevalence studies without analytical component; individual case studies=case report; controlled-clinical trials=group quasi-experimental study; single-subject studies=quasi-experimental study with single subject; pre-existing groups comparisons with covariate analysis=cohort study; one-group pre–post studies=analytical cross-sectional study.

†Rigour was subjectively assessed and based on the number of included participants, amount of collected data and detailed explanation how the study was conducted.

RCT, randomised controlled trial.