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Table 2 Methodological quality (risk of bias) in case-control studies (13 items)

From: Community-onset sepsis and its public health burden: protocol of a systematic review

Definition (Item #) Study 1 {#X} Study 2 {#X} Study 3 {#X} Study 4 {#X} Study 5 {#X} Study 6 {#X} Study 7 {#X}
Internal validity
 The study addresses an appropriate and clearly focused question (Item 1)        
Selection of subjects
 The cases and controls are taken from comparable populations (Item 2)        
 The same exclusion criteria are used for both cases and controls (Item 3)        
 What percentage of each group (cases and controls) participated in the study? (Item 4)        
 Comparison is made between participants and non-participants to establish their similarities or differences (Item 5)        
 Cases are clearly defined and differentiated from controls (Item 6)        
 It is clearly established that controls are non-cases (Item 7)        
 Measures will have been taken to prevent knowledge of primary exposure influencing case ascertainment (Item 8)        
 Exposure status is measured in a standard, valid and reliable way (Item 9)        
 The main potential confounders are identified and taken into account in the design and analysis (Item 10)        
Statistical analysis
 Confidence intervals are provided (Item 11)        
Overall assessment of the study
 Taking into account clinical considerations, your evaluation of the methodology used, and the statistical power of the study, do you think there is clear evidence of an association between exposure and outcome? (Item 12)        
 Are the results of this study directly applicable to the patient group targeted by this guideline? (Item 13)        
Summary quality (risk of bias) rating        
  1. Possible responses to each item: yes, no, can’t say, or doesn’t apply
  2. ≥10 items rated as ‘yes’ - high quality++ (little or no risk of bias; results unlikely to be changed by further research)
  3. 5–9 items rated as ‘yes’ - acceptable quality+ (most criteria met; some flaws in the study with an associated risk of bias; conclusions may change in the light of further studies)
  4. 0–4 items rated as ‘yes’ - low quality 0 (either most criteria not met, or significant flaws relating to key aspects of study design; conclusions likely to change in the light of further studies)