Sem 2 (2)

Question 1

Prevalence
What is it?
What does it describe?
Type of risk?

Answer 1

Proportion of people who have a disease at a given point in time

Burden of a disease

Absolute

Question 2

Prevalence equation
Reported as a …?
Useful for?

Answer 2

No people with disease/total population

Proportion - 200 per 300 people have MS in the UK

Resource allocation

Question 3

Incidence
What is it?
Type of risk?

Answer 3

Number of new cases of a disease within a given time frame

Absolute

Question 4

Incidence
Equation?
Reported as a …?
Useful for measuring?

Answer 4

No new cases/sum of patient time at risk

Rate - 50 per 100 diagnosed with MS in the UK in the last week

Monitoring epidemics

Question 5

Incidence rate ratio
What is it?
Type of risk?

Answer 5

Compares the incidence rate in one group to
another to see if exposure is associated with a
condition

Relative

Question 6

Incidence rate ratio equation
Incidence disease and exposed/unexposed equations

Answer 6

IRR = IR in group 1/IR in group 2

ID E = exposed with disease/total exposed

ID UE = unexposed with disease/total unexposed

Question 7

Risk ratio
When can it be measured?
Type of risk?

Answer 7

In a cohort study where there is a consistent follow up for all patients

Relative

Question 8

Risk ratio equation

Answer 8

Absolute RR for group A/absolute RR for group B

Question 9

Odds ratio
What is it?

Answer 9

Relative comparison of the odds of disease
in one group compared to another group

Question 10

Odds ratio equation

Answer 10

Odds of group A/odds of group B

(Odds of a group = disease/no disease)

Question 11

If the odds ratio is less than 1 what does this mean?
When would this be ideal?

Answer 11

The numerator has a lower odds of the event

If the event is a bad outcome

Question 12

Risk difference
What is it?
Equation?
What does it mean if the calculation is 0?

Answer 12

The difference in risk of the event in group A
compared to group B

Absolute risk of group A - AR of group B

No difference

Question 13

Person years
What is it?

Answer 13

Sum of the total time of everybody followed up in a study

300 people followed up for 3 years = 900 person years

Question 14

95% confidence interval
What is it?

Answer 14

The range within which we can be 95% certain that the true value of the underlying tendency
lies e.g. 0.59 to 1.14

Question 15

The true rate ratio has a 95% probability of lying between what?

Answer 15

0.59 and 1.14

Question 16

In the 95% confidence interval where does the observed data always lie?

Answer 16

Within the confidence interval

Question 17

P<0.05

Answer 17

The null hypothesis value (1) is outside the confidence interval

So it is statistically significant

So reject null

Question 18

P>0.05

Answer 18

The null hypothesis value (1) is inside the confidence interval

So not statistically significant

So fail to reject the null

Question 19

When is the 95% confidence interval wider? (2)

Answer 19

• Greater variation in population values
• Smaller sample size

Question 20

95% confidence interval equation

Answer 20

(OR/ef) to (OR x ef)

Lower limit to upper limit

Question 21

It the confidence interval spans over one what does this suggest?

Answer 21

The findings are not statistically significant

Question 22

Issues with hypothesis testing (2)

Answer 22

• P value <0.05 is arbitrary
• Statistical significance doesn’t equate to clinical significance

Question 23

What does statistical significance not equate to?

Answer 23

Clinical significance