How large was the treatment effect?
The most common way of expressing this is the Relative Risk Reduction (RRR).
In other words, if 20% of the control group died without the treatment
and only 15% of the treatment group died then the RRR = (20 - 15)/20 = 25%
A better, way of presenting the results would be as an Absolute
Risk Reduction (ARR) as it would better reflect the rarity of the outcome.
In this case the AAA = (20 - 15) = 5%
Application to Pollock et al's
thyroxine paper
In this study, the outcomes were measured and reported improvements in
psychological functioning. There were no significant improvements seen, but
the numbers were small. A larger study would be needed to
increase confidence in the results.