Table 4

Association between study characteristics and risk of bias

CharacteristicAll studies (n)Studies in high risk of bias in at least one domain number (%)p Value*
Year of publication0.37
 Pre-20023717 (46%)
 2002–20064620 (44%)
 2007–20105932 (54%)
Type of diabetes0.11
 Type 193 (33%)
 Type 28036 (45%)
 Both3416 (47%)
 Unclear1914 (74%)
Unit of allocation0.24
 Patient9449 (52%)
 Cluster (eg, provider/clinic)4820 (42%)
 The USA or Canada7941 (52%)
 The UK or Western Europe4017 (43%)
 Other2311 (48%)
Journal impact factor0.87
 Greater than 3 (median)7134 (47.9%)
 Less than 3 (median)7135 (49.3%)
Effective sample size0.87
 Greater than 154 (median)7135 (49.3%)
 Less than 154 (median)7134 (47.9%)
Intervention type0.17
 Multifaceted (featuring more than one QI strategy)12463 (51%)
 Single intervention186 (33%)
  • *Comparing proportion of studies with at least one domain at high risk of bias against studies no domains at high risk of bias. For year of publication, Cochran-Armitage test for trend was conducted. For other study characteristics, χ2 (or Fisher's exact) tests for categorical and Wilcoxon signed-rank tests for continuous variables were used.

  • QI, quality improvement.