Table 2 Scientific strength of evidence
From: Italian guidelines for primary headaches: 2012 revised version
+++ | The difference in the parameters of efficacy registered in studies compared with placebo or another active drug has a high level of significance (p < 0.01; p < 0.001; p < 0.0001). Adverse events are rare or occasional and not severe |
++ | The difference in the parameters of efficacy registered in studies reaches the minimum level of significance (p < 0.05) or the minimum clinically significant level (difference in the parameters <15 %)a |
+ | The difference in the efficacy parameters between the study drug and placebo or another active drug is not statistically significant |
0 | The drug is not efficacious or is characterized by severe adverse events |