Select a small number of characteristics

The likelihood of a false positive result among subgroup analyses and meta-regression increases with the number of characteristics investigated. It is difficult to suggest a maximum number of characteristics to look at, especially since the number of available studies is unknown in advance. If more than one or two characteristics are investigated it may be sensible to adjust the level of significance to account for making multiple comparisons. The help of a statistician is recommended (see Chapter 16, Section 16.7).