Table 3 Quality ratings for 7 cohort studies and 6 cross-sectional studies included on the basis of Newcastle-Ottawa quality assessment scale

Representativeness of exposed cohort

Selections of non-exposed cohort

Assessment of exposure

Absence of outcome at start of study

Comparability

Assessment of outcome

Follow-up period (≥6 months)

Adequacy of follow-up

Total score out of 9 points

Ball et al., 2006

1

1

1

1

1

1

1

1

9 (high)

Edwards et al., 2010

1

1

1

1

2

0

1

1

8 (high)

Emerson et al., 2012

1

1

1

1

2

1

1

1

9 (high)

Gill et al., 2012

1

1

1

1

2

0

1

1

8 (high)

Marottoli et al., 1994

1

1

1

1

2

0

1

1

8 (high)

Sims et al., 2007

1

1

1

1

2

0

1

1

8 (high)

Woolnough et al., 2013

1

1

1

1

0

1

1

1

7 (medium)

Representativeness of sample

Sample size

Non-respondents

Ascertainment of primary measurement

Comparability

Ascertainment of the outcome

Total score out of 10 points

Carr et al., 2011

1

0

0

2

0

2

6 (medium)

Classen et al., 2013

1

0

0

2

2

2

8 (high)

Davis et al., 2011

1

0

0

2

2

2

8 (high)

Dawson et al., 2010

1

0

0

2

2

2

8 (high)

Langford et al., 2013^a

1

1

0

2

0

1

6 (medium)

Stav et al., 2008

1

0

0

2

2

2

8 (high)