RESS

Question 1

Incidence rate?

Answer 1

Incidence rate = Number of new cases in period / Number at risk in population in period

Question 2

Prevalence rate?

Answer 2

Prevalence rate= No. of people with a disease at certain time / No. of people in the population at certain time

Question 3

Case fatality rate?

Answer 3

Case fatality rate = No. of people who die from the disease in period / No. of people with disease in period

Question 4

Mortality rate?

Answer 4

Mortality rate = No. of people who die from the disease in period / No. of people who die in period

Question 5

How is adjustment done to better represent the crude rates? (eg age adjustment)

Answer 5

It is done by calculating the stratum specific rates. A stratum is a subgroup in the sample, eg) age or sex group

Question 6

Risk of disease?

Answer 6

Risk = Number or new cases / Number at risk

Question 7

What does risk ratio measure?

Answer 7

It measures relative risk (RR)

Question 8

Risk ratio?

Answer 8

Those with disease and exposed to risk factor / All those exposed to risk factor
DIVIDED BY:
Those with disease and not exposed to risk factor / All those not exposed to risk factor

Question 9

What does it mean if the relative risk is:
=1 ?
<1 ?
>1 ?

The further away the relative risk is from 1, the stronger the association

Answer 9

= 1 … the risk in the exposed group is the same as the risk in the unexposed group
<1 … the exposure is associated with a protective effect
>1 … the exposure is associated with harm

Question 10

What is an Odds ratio?

Answer 10

A measure that represents the relative risk for a case-control study

Question 11

What does it mean if the odds ratio = 1?

Answer 11

The probability of an event occuring is the same as the probability that the event does not occur (ie an event will occur half the time)

Question 12

What is the Null hypothesis (H0)?

Answer 12

Assumes no effect (if the drug is tested, the H0 will be that the drug will have no effect)

Question 13

What is the Alternative hypothesis (H1 or Ha)?

Answer 13

Assumes there is an effect, either beneficial or harmful, ie. two-sided.

Question 14

What are the features of a hypothesis?

Answer 14

It must be:

• Plausible
• Falsifiable (able to be accepted or rejected),
• Have direction
• Be precise

Question 15

What is the P value?

Answer 15

It is the probability of obtaining the results of the test given that the null hypothesis is true, (ie- how likely it is that the null hypothesis is correct)
So: the smaller the p value, the less likely the result is to have occurred by chance alone & thus more likely the result is due to exposure

Question 16

What are the features of Survival data?

Answer 16

• A person enters the study
• The time the person leaves the study (therefore the event= failure)
• Leaving the study before the event occurs, or entering after the start of the study (=censoring)

Question 17

How may survival data be either Right or Left censored?

Answer 17

Right censored= people in the study didn’t reach a failure before the end of the study (eg in new HIV drug trial, right censored data will occur if the study participants die of other non-AIDS causes)
Left censored= not certain what happened to the people before the time at which they entered the study (eg when they already have the disease of interest when the study starts)

Question 18

What is:

a) Survival function
b) Hazard function

Answer 18

a) =the chance of survival until a certain time

b) =the chance of instantaneous failure at any one time

Question 19

What does a Kaplan-Meier plot show?

Answer 19

It shows survival as a series of steps. It steps down every time a failure is observed.

Question 20

What is a Log rank test?

Answer 20

(to examine Surviving data) This compares the survival functions between the 2 groups.

Question 21

What is the Asch Experiment (1952)?

Answer 21

What others think can change our behaviour – everyone asked a question, rest of group answer wrong, participant agrees with the wrong answer.

Question 22

What is social marketing?

Answer 22

Might be used to address lack of knowledge, marketing an idea NOT a product, e.g. advertising the number of units in alcohol in order to lower people’s drinking

Question 23

What is the Social norms approach?

Answer 23

It is about adressing misperceptions of the norm, reflecting a positive behaviour fact about the population.
1.Understand the norm –>2.Understand what people believe is the norm –>2.Evidence of mismatch (misperception) –>4.Challenge misperceptions

Question 24

How are themes identified?

Answer 24

• Immersing in the data
• Coding transcripts
• Organising codes into meaningful groups
• Generating themes

Question 25

Why are themes different to categories?

Answer 25

Themes are broader and include interpretation about a phenomenon

Question 26

What is Sensitivity?

Answer 26

The proportion of people with the disease who are identified as having it by a positive test result.
Sensitivity = A/(A+C)

Question 27

What is Specificity?

Answer 27

The proportion of people without the disease who are correctly re-assured by a negative test result.
Specificity = D/(D+B)

Question 28

What is a positive predictive value?

Answer 28

The probability that a person with a positive test result actually has the disease
Positive predictive value = A/(A+B)

Question 29

What is a negative predictive value?

Answer 29

Probability that a person with a negative test result doesn’t have the disease
Negative predictive value = D/(C+D)

Question 30

What are some features of high sensitivity?

Answer 30

• Maximises identification of diseased people in the screened population
• Few false negatives
• Lots of false positives

Question 31

When is high sensitivity desirable?

Answer 31

If the adverse consequences of missed diagnosis for the individual are worse than early diagnosis
-If serious consequences of missed diagnosis on society

Question 32

Features of high specificity?

Answer 32

• Tends to detect only people with the disease
• Relatively few false positives
• Lots of false negatives

Question 33

When is high specificity desirable?

Answer 33

• If the diagnosis is associated with anxiety or stigma

- Further investigations are time consuming/expensive