An interesting article was published in the British Medical Journal in April. Researchers looked at the influence of sample size on treatment effect estimates. The bottom line is that they found that treatment effect estimates were significantly larger from smaller trials as compared to larger trials (up to 48% greater!). The figure below shows this relationship. The left graph compares sample sizes from each study broken into quartiles and on the right arbitrary divisions by raw numbers.
So what does this mean for the average reader of medical journals? Pay attention to sample size. Early studies on new technology (whether meds or procedures) are often carried out on a fairly small group of people. Realize that what you see is likely overestimated (compared to a large study). If benefits are marginal (barely clinically significant) realize they likely will go away with a larger trial. If benefits are too good to be true….they likely are too good to be true and you should temper your enthusiasm. I always like to see more than one trial on a topic before I jump in and prescribe new meds or recommend new procedures.