Table 3

Study quality assessed by the modified Downs and Black checklist

Bantoft et al 21 Botter et al 13 Commissaris et al 25 Cox et al 14 Gilson et al 18 Kruse et al 17 Ohlinger et al 20 Mullane et al 19 Sliter and Yuan10 Straker et al 15 Tronarp et al 16 Zeigler et al 8
1 Is the hypothesis/aim/objective of the study clearly described? 111111111111
2 Are the main outcomes to be measured clearly described in the introduction? or
Methods section?
3 Are the characteristics of the patients included in the study clearly described? 111111111111
4 Are the interventions of interest clearly described? 111111111111
5 Are the distributions of principal confounders in each group of subjects to be compared clearly described? 202012220112
6 Are the main findings of the study clearly described? 111111111111
7 Does the study provide estimates of the random variability in the data for the main outcomes? 111111111111
8 Have all important adverse events that may be a consequence of the intervention been reported? 101001110000
9 Have the characteristics of patients lost to follow-up been described? 000010011011
10 Have actual probability values been reported (eg, 0.035 rather than <0.05) for the main outcomes except where the probability value is less than 0.001? 111111111111
External validity
11 Were the subjects asked to participate in the study representative of the entire population from which they were recruited? 110000101111
12 Were those subjects who were prepared to participate representative of the entire population from which they were recruited? 110000100011
13 Were the staff, places and facilities where the patients were treated representative of the treatment the majority of patients receive? 001000000000
Internal validity—bias
14 Was an attempt made to blind study subjects to the intervention they have received? 000000000000
15 Was an attempt made to blind those measuring the main outcomes of the intervention? 000100000000
16 If any of the results of the study were based on ‘data dredging’, was this made clear? 111111111111
17 In trials and cohort studies, do the analyses adjust for different lengths of follow-up of patients, or in case–control studies, is the time period between the intervention and outcome the same for cases and controls? 101111111111
18 Were the statistical tests used to assess the main outcomes appropriate? 111111111111
19 Was compliance with the intervention/s reliable? 111111111111
20 Were the main outcome measures used accurate (valid and reliable)? 111111111111
Internal validity—confounding (selection bias)
21 Were the patients in different intervention groups (trials and cohort studies) or were the cases and controls (case–control studies) recruited from the same population? 110000101110
22 Were study subjects in different intervention groups (trials and cohort studies) or were the cases and controls (case–control studies) recruited over the same period of time? 000000000000
23 Were study subjects randomised to intervention groups? 111110110011
24 Was the randomised intervention assignment concealed from both patients and healthcare staff until recruitment was complete and irrevocable? 000000000000
25 Was there adequate adjustment for confounding in the analyses from which the main findings were drawn? 100001010010
26 Were losses of patients to follow-up taken into account? 010010011011
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%? Sample sizes have been calculated to detect a difference of x% and y%. 000000101010
Total score19/2816/2817/2814/2816/2816/2820/2819/2817/2815/2821/2819/28
  • *Item has been modified ‘yes’=1; ‘no’=0.