Tutorials

Question 1

What can be estimated from a sample?

Answer 1

The true underlying risk in a population can be calculated

Question 2

What is a p value?

Answer 2

Probability of obtaining the study result to see whether the null hypothesis is true

Question 3

What does it mean if p<0.05?

Answer 3

Null hypothesis is rejected and results are statsistically significant and not due to chance

Question 4

What is the procedure of hypothesis testing?

Answer 4

1. Set up a null hypothesis (e.g. difference in prevalence between the two groups is zero)
2. Choose an appropriate statistical test
3. Inspect the results (estimated measure of association – or, in this case, estimated
4. difference in prevalences – plus its CI and P value) for evidence of real difference: can we reject the null hypothesis?

Question 5

What are ‘odds’?

Answer 5

The odds is another way to express probability, e.g. the odds of exposure is the number of people who have been exposed divided by the number of people who have not been exposed.

Question 6

What is the mathematical relationship between odds and probability?

Answer 6

Odds= probability/ (1-probability)

Question 7

What is the relative risk?

Answer 7

A measure of association between exposure and disease. It is the ratio of the incidence in exposed group/ incidence in non exposed

Question 8

What does a relative risk of 1.0 mean?

Answer 8

The incidence of disease in exposed and unexposed are equal

Question 9

What does a relative risk greater than 1.0 mean?

Answer 9

Positive association- increased risk among those exposed

Question 10

What does a relative risk less than 1.0 mean?

Answer 10

There is a decreased risk among the exposed

Question 11

What is attributable risk?

Answer 11

Measure of exposure effect that indicates on an absolute scale how much greater the frequency of disease in the exposed group is than the unexposed, assuming relationship is causal

Question 12

How do you calculate attributable risk?

Answer 12

Incidence in exposed - incidence in the unexposed

Question 13

How do you calculate the odds ratio?

Answer 13

odds of exposure in cases/ odds of exposure in control

Question 14

What is the odds ratio?

Answer 14

In case control studies you can’t calculate the incidence of disease in exposed and non exposed so you calculate the odds of exposure (See notes).

Question 15

What does an odds ratio of 1 indicate?

Answer 15

exposure is no more likely in cases than controls

Question 16

What does an odds ratio of more than 1 mean?

Answer 16

Exposure is more likely in the case group

Question 17

what does an odds ratio of less than 1 mean?

Answer 17

Exposure is less likely in the case group

Question 18

how can you deal with confounding variables?

Answer 18

Stratification, standardisation, regression
§ Stratification- a method for controlling the effect of confounding at the analysis stage of a study - risks are calculated separately for each category of confounding variable, e.g. each age group and each sex separately.

§ Standardisation- a method for controlling the effect of confounding at the analysis stage of a study. Used to produce a Standardised Mortality Ratio, a commonly used measure in epidemiology.

§ Regression- a method for controlling the effect of confounding at the analysis stage of a study - statistical modelling is used to control for one or many confounding variables.