An excellent reference to compare the effectiveness of different drug treatments is a measure called Numbers Needed To Treat (NNT). This is the number of patients who need to be treated to achieve one additional favourable outcome.

NNT is calculated using the formula 1 / absolute risk reduction (where / = divided by), and it is accompanied by a 95% confidence interval. For instance, if 75% of patients have adequate analgesia with treatment (EER - Experimental Event Rate) and 25% with control (CER - Control Event Ratio), the NNT is 1 / (0.75-0.25 = 1/0.5 = 2). Absolute Risk Reduction = (EER - CER).

The NNT has to specify treatment, control, outcome and duration of treatments and effects. For example, using Ibuprofen, if for every 100 patients with acute pain treated with Ibuprofen, 37 will have an adequate pain relief because of the Ibuprofen we have given them, then we have to treat 100/37 or 2.7 patients with Ibuprofen for one to benefit because of the Ibuprofen they have been given. This equals the Numbers Needed to Treat.  

The best NNT would be 1. The NNT is a useful tool for comparing two similar treatments. When the NNT is above 10, the effectiveness of the treatment is doubtful.

The table below shows the NNTs for some of the pain management treatments.

The Oxford League Table of Analgesic Efficiency

(commonly used analgesic doses)

This indicates at least 50% pain relief

 
Source: Bandolier: Acute Pain Management Scientific Evidence, 2nd Edition, 2005: The Oxford League Table of Analgesic Efficiency