The influence of age on sample size calculation in acute pain trials using morphine consumption as an end point

Many trials in acute postoperative pain use morphine consumption as an end point. Age has been shown to have a significant influence on morphine consumption but is rarely considered in end point analysis.

Simulation was used to investigate the effect of age on the power of various sample sizes to detect differences in morphine consumption in control and study groups.

The sample sizes required for 80% power were approximately twice that predicted by a sample size program when comparing morphine consumption using a t test without adjustment for age.

The model suggests that variations in age have a profound effect on sample size. Researchers may need to account for this to prevent both type 1 and type 2 error.