Module 07 Summary

What this module established

The best effect size is the one that needs no explaining: 17.3 ms saved, interval 6.9 to 27.8, tells a decision-maker more than any standardised measure.

Carry forward

• Cohen's d responds to the spread as much as to the gap. The same 7.4-point gap gave d = 0.44 on one population and d = 1.45 on a less variable one — a factor of 3.3 from the spread alone.
• Odds ratios and risk ratios agree only when the outcome is rare. With a common outcome a risk ratio of 1.50 came with an odds ratio of 2.25.
• Two studies can both reject the null and only one tell you the effect size — the small one's interval was 6.6 times wider.
• With 50,000 per group a 0.283-point difference was significant at p = 0.003 with the whole interval below the 2-point bar. The study ruled a meaningful effect out.

Before moving on

Move on when you have stated the smallest effect worth acting on and compared the whole interval to it.

Mark complete