Table 6 Risk of bias for non-randomised studies using the QATSQ tool

Bapat, Jorm and Lawerence [67]

2

Participants are very likely to be representative

Cannot tell the percentage of participants who agreed

2

Study is designated as a cohort analytic study

3

There were gender and age differences that may have influenced the outcomes between participants and these were not controlled for in analysis

3

Outcome assessors knew intervention status, and blinding of participants to research question is not described

3

The validity and reliability of the instruments are not described

3

Withdrawals and dropouts were not described

Weak quality: as this study scored four weak ratings, the overall judgement is weak quality

Breslin et al. [37]

2

Participants are very likely to be representative

Cannot tell percentage of participants who agreed.

1

Study is designated as a controlled clinical trial

1

Confounders (gender, sport type) were similar across control and intervention groups

2

Cannot tell if outcome assessors were aware of intervention status and cannot tell if intervention participants were aware of research question

1

Tools were shown to be valid and reliable.

3

Cannot tell if there were withdrawals or dropouts

Moderate quality: As this study scored one weak rating the overall judgement is moderate quality

Donohue et al. [68]

1

Participants are very likely to be representative

All participants agreed to participate

2

Study is designated as a cohort analytic study

3

There were gender, ethnic and age differences that may have influenced the direction of result. These were not controlled for in the analysis

3

Outcome assessors knew intervention status, and the participants knew intended outcome of the research (i.e. developing intervention)

1

The validity and reliability of the instruments is described

2

There was a 70% follow-up rate from those that consented and completed the intervention

Weak quality: as this study scored two weak ratings, the overall judgement is weak quality

Pierce, et al. [71]

2

Participants are very likely to be representative

Cannot tell the percentage of participants who agreed

2

Study is designated as a cohort analytic study

3

There were age and education differences that may have influenced the direction of result these were not controlled for in the analysis

3

Outcome assessors knew intervention status, and the participants knew intended outcome of the research (i.e. respond to mental health problems)

3

The validity and reliability of the instruments is not described

2

There was a 66% follow-up rate from those that consented and completed the intervention

Weak quality: as this study scored three weak ratings, the overall judgement is weak quality

Longshore and Sachs [70]

1

Participants are very likely to be representative

Above 80% of participants agreed to participate

1

Study is designated as a controlled clinical trial.

1

No significant differences were found between the groups before the intervention

3

Outcome assessors knew intervention status, and the participants knew intended outcome of the research (i.e. benefits of mindfulness)

3

The validity and reliability of the instruments is not described

1

There was a > 80% follow-up rate from those that consented and completed the intervention

Weak quality: as this study scored two weak ratings, the overall judgement is weak quality

Sebbens et al. [29]

1

Participants are very likely to be representative

Above 80% of participants agreed to participate

1

Study is designated as a controlled clinical trial.

1

No significant demographic differences were found between the groups before the intervention

3

Outcome assessors knew intervention status, and blinding of participants to research question is not described

3

The validity and reliability of the instruments is not described

1

There was a > 80% follow-up rate from those that consented and completed the intervention

Weak quality: As this study scored two weak ratings, the overall judgement is weak quality

Slack et al. [72]

1

Participants are very likely to be representative

Above 80% of participants agreed to participate

2

Study is designated as a cohort analytic study

3

Confounding variables were not discussed

3

Outcome assessors knew intervention status, and blinding of participants to research question is not described

3

While one measure was referenced as valid and reliable, no information was reported on validity and reliability of another measure (RSMT)

1

There was a > 80% follow-up rate from those that consented and completed the intervention

Weak quality: As this study scored three weak ratings, the overall judgement is weak quality

Tester, Watkins and Rouse [73]

2

Participants are very likely to be representative

Cannot tell the percentage of participants who agreed

2

Study is designated as a cohort analytic study

3

Confounding variables were not discussed

2

Cannot tell if outcome assessors were aware of intervention status

Cannot tell if intervention participants were aware of research question

1

Tools were referenced as valid and reliable

3

Cannot tell if there were withdrawals or dropouts

Weak quality: As this study scored two weak ratings, the overall judgement is weak quality

Summary of bias across the studies

Four studies were of strong quality and controlled for selection bias, the remaining 4 were of moderate quality

Three studies were of strong quality for study design, and the remaining 5 were of moderate quality

Most studies (n = 5) did not control or disclose information on confounders and were designed weak quality. The following three were designated as strong, with sufficient information provided

Seventy five percent of the non-randomised studies were of weak quality for blinding participants and outcome assessors. Fifteen percent were of moderate quality

Three studies were of strong quality and referenced adequate validity for outcome measures, while 5 studies did not describe validity, resulting in weak quality

There was a mixture of strong (n = 3), weak (n = 3) and moderate (n = 2) for the researchers disclosure of follow-up rates and dropouts

On two outcomes (selection bias and study design), the included studies were of strong or moderate quality. There was a combination of strong and weak scores for confounding variables and outcome measures and moderate and weak for blinding. Mixed findings were indicated for withdrawal rates, comprising a range of strong, moderate and weak studies