Understanding evidence The big picture Systematic reviews are
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.
Forest Plot Main Graph Favours Treatment A Favours Comparator B Trial 1 Trial 2 Trial 3 Trial trials 4 Many similar Trial 5 Trial 6 Trial 7 Trial 1+2+3 +4+5+6+7 Relative Risk (RR)
Steroids given before preterm delivery reduce the number of babies who die.
Favours steroid Favours placebo "No difference" RR=1 10% 5% die 10% die with steroid 10% 5% die 10% die with placebo RR RR = = ? ? 0. 01 0. 5 1 2 10 Relative Risk (RR) of Death Relative Risk (RR) of death
Trial Deaths Babies #1 1070 Steroid Favours steroid Favours placebo Placebo 6. 8% 11. 2% 0. 01 = 0. 61 0. 5 1 2 10 Relative Risk (RR) of Death of death
Trial Babies #1 1070 Deaths Steroid Placebo Favours Point steroid Favours placebo estimate "best guess at truth" 6. 8% 11. 2% 95% Confidence interval "truth probably in here" 0. 01 0. 5 1 2 10 Relative Risk (RR) of Death of death
Trial Babies Deaths Steroid Favours steroid Favours placebo Placebo #1 1070 6. 8% 11. 2% #2 130 1. 4% #3 126 3. 0% 11. 9% #4 127 9. 0% 10. 0% #5 146 1. 4% #6 144 2. 5% 15. 9% #7 743 9. 7% 10. 0% 8. 2% 6. 7% Total 2486 0. 01 0. 5 1 2 10 Relative Risk (RR) of Death of death
0. 1 0. 5 1 2 10
Favours steroids Deaths Year Babies Steroid Placebo 1972 1070 36 60 1977 1200 37 65 1978 1326 39 72 1979 1453 44 79 1979 1599 45 84 1980 1743 47 94 1981 2486 83 131 Favours placebo "Cumulative Meta-analysis" 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
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