Meta Analysis

Question 1

What is Meta analysis?

Answer 1

Process of using statistical methods to combine the results of different studies

• integrate the findings
• pool data
• identify overall trends

It is an optional part of a systematic review

Question 2

Advantages of Meta analysis?

Answer 2

Increase in power

Improvement in precision

Answer questions not posed by individual studies

Question 3

When should meta analysis only be undertaken?

Answer 3

Minimal differences in characteristics across studies

Same outcome measure

Data in each study is fully available

• otherwise potential ton mislead

Question 4

Types of data in meta analysis?

Answer 4

Dichotomous data
- died or not
- born or not
- illness or not

Continuous data
- blood pressure
- weight
- amount of pain

Question 5

What is OR?

Answer 5

ODDS RATIO

• measure of how strongly an event is associated with exposure

E.g. smoking and lung cancer

• 17 smokers / 100 have lung cancer, 83 / 100 do not
• 1 non smoker / 100 has lung cancer, 99 / 100 do not

17/83 = 0.205
1/99 = 0.01

Odds in exposed group / odds in non exposed group
0.205 / 0.01 = 20.5
Smokers 20x more likely according to this odds ratio

Question 6

What is RR?

Answer 6

Risk ratio / relative risk

Determines risk of incidence of something in one group vs another group of data.

E.g. wound infection after incidental appendectomy

Had appendectomy
- yes, 7 infections and 124 non infection. 7/131 = 5.34%
- no, 1 infection and 78 non. 1/79 = 1.27%

RR = 5.34 - 1.27 = 4.2

4.2x the risk of infection compared to those who did not have surgery

If RR is <1 then shows there is a decrease in risk

Question 7

What is RRR?

Answer 7

Relative risk reduction

• shows how much an intervention / treatment has reduced the risk of bad outcomes

1 - RR

Question 8

What is ARD?

Answer 8

Risk of developing cancer in smokers = 0.48 e.g.

Risk non smokers = 0.2 e.g.

Risk difference = 0.28
- smoking adds this 0.28 risk or 28%

Question 9

How calculate confidence interval?

Answer 9

CI = mean value plus/minus Z-value for CI

Multiplied by

S/root N