Table 3. Assessment of study quality by means of the Downs and Black checklist⁴².

Questions (Q)		Aydemir et al.21		Härtel et al.9		Abu-Maziad et al.22		Auriti et al.23		Koroglu et al.24		Spiegler et al.25		Abdel-Hady et al.26		Bertalan et al.27		Reiman et al.28		Dzwonek et al.29		van Der Zwet et al.30		Schueller et al.31		Derzbach et al.32		Härtel et al.33		Baier et al.34		Göpel et al.35		John Baier et al.36		Hedberg et al.37		Ahrens et al.38		Bessler et al.39		Harding et al.40		Treszl et al.41
Q 1		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 2		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 3		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 4		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 5		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 6		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 10		no		yes		yes		yes		yes		yes		yes		yes		yes		yes		no		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		no
Q 11		no		no		no		yes		no		no		no		no		no		no		yes		no		no		no		no		no		no		no		no		no		no		no
Q 13		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 14		no		no		no		no		no		no		no		no		no		no		no		yes		no		no		yes		no		no		no		no		no		yes		no
Q 15		no		no		no		no		no		no		no		no		no		no		no		yes		no		no		yes		no		no		no		no		no		yes		no
Q 18		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 20		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 21		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		no		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 22		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 25		no		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes		no		yes		yes		yes		yes		yes		yes		yes		yes		yes		yes
Q 27		no		yes		yes		no		yes		no		no		no		yes		no		no		no		no		yes		yes		no		no		no		yes		no		yes		no

Down and Black checklist for assessing study quality. Q 1 = Is the hypothesis/aim/objective of the study clearly described?; Q 2 = Are the main outcomes to be measured clearly described in the Introduction or Methods section?; Q 3 = Are the characteristics of the patients included in the study clearly described?; Q 4 = Are the interventions of interest clearly described?; Q 5 = Are the distributions of principal confounders in each group of subjects to be compared clearly described?; Q 6 = Are the main findings of the study clearly described?; Q 7 = Does the study provide estimates of the random variability in the data for the main outcomes?; Q 8 = Have all important adverse events that may be a consequence of the intervention been reported?; Q 9 = Have the characteristics of patients lost to follow-up been described? Q 10 = Have actual probability values been reported (e.g. 0.035 rather than < 0.05) for the main outcomes except where the probability value is less than 0.001?; Q 11 = Were the subjects asked to participate in the study representative of the entire population from which they were recruited?; Q 12 = Were those subjects who were prepared to participate representative of the entire population from which they were recruited?; Q 13 = Were the staff, places, and facilities where the patients were treated, representative of the treatment the majority of patients receive?; Q 14 = Was an attempt made to blind study subjects to the intervention they have received?; Q 15 = Was an attempt made to blind those measuring the main outcomes of the intervention?; Q 16 = If any of the results of the study were based on "data dredging", was this made clear?; Q 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?; Q 18 = Were the statistical tests used to assess the main outcomes appropriate?; Q 19 = Was compliance with the intervention/s reliable?; Q 20 = Were the main outcome measurements used accurate (valid and reliable)?; Q 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?; Q 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?; Q 23 = Were study subjects randomized to intervention groups?; Q 24 = Was the randomized intervention assignment concealed from both patients and healthcare staff until recruitment was complete and irrevocable?; Q 25 = Was there adequate adjustment for confounding in the analyses from which the main findings were drawn?; Q 26 = Were losses of patients from follow-up taken into account?; Q 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%? Note: Questions 7, 8, 9, 12, 16, 17, 19, 23, 24 and 26 were considered to be not applicable to the type of studies included in this in-depth review.