Understanding evidence: The big picture Systematic reviews are the best way to understand the effects of treatments because they consider all the relevant, reliable evidence. These slides will teach you how to interpret the main graph used to present the results of a systematic review of randomized trials. main graph

Forest Plot Main Graph Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Favours Treatment A Favours Comparator B Main Graph Many similar trials Trial 2 Trial 3 Trial 1 Trial 5 Trial 6 Trial 7 Trial 4 Trial 1+2+3 +4+5+6+7 Relative Risk (RR)

Steroids given before preterm delivery reduce the number of babies who die.

Relative Risk (RR) of Death Favours steroid Favours placebo 11.2% RR = percent who died with placebo percent who died with steroid "No difference" RR=1 5% die with steroid 10% die with placebo RR = ?? 10% die with steroid 5% die with placebo RR = ?? 10% die with steroid 10% die with placebo RR = ?? 0.01 0.1 0.5 1 10 2 Relative Risk (RR) of Death Relative Risk (RR) of death

Relative Risk (RR) of Death Favours steroid Favours placebo #1 Trial Deaths Deaths Babies 1070 Steroid Placebo 6.8% 11.2% 11.2% RR = percent who died with placebo percent who died with steroid 6.8% = 0.61 11.2% 0.01 0.1 0.5 1 10 2 Relative Risk (RR) of Death Relative Risk (RR) of death

Relative Risk (RR) of Death Favours steroid Favours placebo Point estimate "best guess at truth" #1 Trial Deaths Babies 1070 Steroid Placebo 6.8% 11.2% 95% Confidence interval "truth probably in here" 0.01 0.1 0.5 1 10 2 Relative Risk (RR) of Death Relative Risk (RR) of death

Relative Risk (RR) of Death Favours steroid Favours placebo #1 Trial Deaths Babies 1070 Steroid Placebo 6.8% 11.2% #2 130 1.4% 8.2% #3 3.0% 11.9% 126 #4 9.0% 10.0% 127 #5 1.4% 6.7% #6 2.5% 15.9% #7 9.7% 10.0% 146 144 743 2486 Total 0.01 0.1 0.5 1 10 2 Relative Risk (RR) of Death Relative Risk (RR) of death

0.1 0.5 1 10 2

Relative Risk (RR) of Death Favours steroids Favours placebo Year Deaths "Cumulative Meta-analysis" Babies Steroid Placebo 1972 1070 36 60 1977 37 65 1200 1978 39 72 1326 1979 44 79 45 84 1980 47 94 1981 83 131 1453 1599 1743 2486 How long did it take to change practice? Another decade and 10 more trials! 0.1 0.5 1 2 10 Relative Risk (RR) of Death