1. 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

2. 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
Relative Risk (RR)

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

4. 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

5. 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

6. 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

7. 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

8. 0.1
0.5 1 10 2

10. 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