| (Pfeiffer, Gutmann et al. 2007) RCT | Measurement bias, Funding bias |
| (Pahwa, Koller et al. 2007) RCT | Sampling bias, Participant/ rater bias, Funding bias |
| (Katzenschlager, Poewe et al. 2018) RCT | Funding bias |
| (Ostergaard, Werdelin et al. 1995) RCT | Sample bias, Blinding bias |
| (Ondo, Hunter et al. 2012) Cohort | blinding, sample bias, reporter, patient bias, |
| (Colzi, Turner et al. 1998) Cohort | Sample, Measurement, Unblinded, No randomisation |
| (Sesar, Fernández-Pajarín et al. 2017) Cohort | Attrition bias, Measurement bias, Unblinded, No randomisation |
| (Isaacson, Lew et al. 2016) Cohort | Funding, Unblinded, No randomisation |
| (Pietz, Hagell et al. 1998) Cohort | Measurement bias, Sample bias, Unblinded, No randomisation |
| (Muguet, Broussolle et al. 1995) | Measurement, reporter, search strategy, design |
| (Setter 2008) | Measurement, reporter, search strategy design |
| (Perez-Lloret and Rascol 2010) | Measurement, reporter, search strategy design |
| (Factor 2004) | Measurement, reporter, search strategy design |
| (van Laar and Borgemeester 2016) | Measurement, reporter, search strategy design |
| (Bhidayasiri, Garcia Ruiz et al. 2016) | Not systematic, excluded studies or inclusion criteria, did not explain risks of bias or study design, nil meta-analysis, reporter, publication, selection bias, omitted bias, statistical and observer |
| (Deleu, Hanssens et al. 2004) | Rater bias, |
| (Clarke, Davies et al. 2000) | Reporter bias - unable to tell if reviewed independently. |
| (Tomlinson, Stowe et al. 2010) | Rater bias, |
| (Bhidayasiri, Chaudhuri et al. 2015) | Rater, measurement, reporter, search strategy, design |
| (Price, Martin et al. 2016) | Nil blinding, selection bias, reporter bias, study design, no control of confounders, nil blinding, nil standardised collection tools, nil statistical analysis |
| (Albanese, Bonuccelli et al. 2001) | Not systematic, no thorough literature search methods mentioned, did not list excluded studies or inclusion criteria, did not explain risks of bias or study design, nil metanalysis, high risk of reporter, publication, selection bias, omitted bias, |
| (Trenkwalder, Chaudhuri et al. 2015) | Rater, reporter, funded, measurement, sample, design, blinding, |
| (Jenner and Katzenschlager 2016) | Rater, measurement, reporter, sample, design, blinding, funding |
