Table 2 Modified Downs and Black critical appraisal checklist applied to observational studies (adapted from Downs and Black [49])

1

Is the hypothesis/aim/objective of the study clearly described?

2

Are the main outcomes to be measured clearly described in the introduction or methods section?

3

Are the characteristics of the participants included in the study clearly described?

4

Removed

5

Are the distributions of principal confounders clearly described?

6

Are the main findings of the study clearly described?

7

Does the study provide estimates of the random variability in the data for the main outcome?

8

Removed

9^*

Have the characteristics of patients lost to follow up been described or did the study have any participant losses?

10

Have actual probability values been reported for the main outcomes, except where the probability value is < 0.001?

11

Were the subjects asked to participate in the study representative of the entire population from which they were recruited?

12

Were those subjects who were prepared to participate representative of the entire population from which they were recruited?

13^*

Were the staff, places, and facilities where the participants were treated or where the testing was performed representative of the exams/treatment the majority would receive?

14

Removed

15

Removed

16

If any of the results of the study were based on “data dredging”, was this made clear?

17

In trials and cohort studies, do the analyses adjust for different lengths of follow-up of participants, or in case-control studies, is the time period between the intervention and the outcome the same for cases and controls?

18

Were the statistical tests used to assess the main outcomes appropriate?

19

Removed

20

Were the main outcome measures used accurate (valid and reliable)?

21

Were the participants in different intervention groups (trials and cohort studies) or were the cases and controls (case-control studies) recruited from the same population?

22^*

Were study subjects recruited over the same period of time?

23

Removed

24

Removed

25

Was there adequate adjustment for confounding in the analyses from which the main findings were drawn?

26

Were losses of patients to follow up taken into account?

27

Did the study have sufficient power to detect a clinically important effect where the probability value for a difference being due to chance is less than 5%?