Week 122 - Measurements in population I

Question 1

What is incidence?

Answer 1

Proportion of a group that will develop a certain disease over a time period

Question 2

What is prevalence?

Answer 2

Amount/proportion of people that have a disease at a given time

Question 3

List the study order of hierachy of evidence?

Answer 3

1) Systematic reviews with at least one RCT
2) RCT
3) Non RCTs
4) Cohort studies
5) Case-control studies
6) Self controlled case series
7) Ecological studies
8) Cross sectional studies of incidence and prevalence
9) Case series and case reports

Question 4

What is an RCT?

Answer 4

A randomised controlled trial

Randomisation of sorting people into groups removes any confounding factors between the intervention group and control group

Question 5

What is a self controlled case series?

Answer 5

A study in which the incidence of a certain outcome is compared to the incidence of the outcome when the individual is not exposed

e.g. occurence of adverse reaction when given a drug compared to when not given

Question 6

What is a cross sectional study?

Answer 6

A study that collects data on incidence/prevalence of a disease in a population at a specific point in time

Question 7

What is an ecological study?

Answer 7

A study in which populations/groups are analysed to study effects of risk factor on health

e.g. rates of obesity in different countries

Question 8

What is the disadvantage of an ecological study?

Answer 8

Hard to control due to confounding variables

Question 9

What is a case report study?

Answer 9

A detailed report of a patient with a condition of interest

Question 10

What is a case series study?

Answer 10

A descriptive study of patients with a known exposure or condition

Question 11

What is a disadvantage of case-series study?

Answer 11

Can involve selection bias

Question 12

List the two types of research studies?

Answer 12

Experimental studies

Observational studies

Question 13

What is an experimental study?

Answer 13

Study which exposure is determined as part of study design

Question 14

What is an observational study?

Answer 14

Study in which exposure is not determined as part of the study design

• already existing expossure and consequences are studied

Question 15

Give an example of an experimental study?

Answer 15

RCTs

Non-randomised trials

Question 16

What is the null hypothesis?

Answer 16

Statement being tested in a test of hypothesis

Question 17

What is the alternative hypothesis?

Answer 17

What is believed to be true if the null hypothesis is false

Question 18

What is a case control study?

Answer 18

A study which starts with the identification of people:

• with the disease of interest, and a
• control group without the disease

Question 19

What is a retrospective case control study?

Answer 19

A case control study which starts with the case and looks back at exposure to see if there is an associated risk

Question 20

What is a prospective case control study?

Answer 20

A case control study which recruit individuals as they develop the disease of interest

Question 21

What is a p-value?

Answer 21

Probability of observing a difference as large as previously seen in a study due to chance

p-value < 0.05 => statistically significant

Question 22

What is a cohort study?

Answer 22

A study that starts by looking at a certain group of people and identifies those who are exposed to the risk factors and those who are not.

It then compares the incidence of disease development between the two exposure groups.

Question 23

What is the difference between a prospective and retrospective cohort study?

Answer 23

Prospective = current exposure

Retrospective = identifies “past” exposure to risk factors

Question 24

What are the advantages of a case control study?

Answer 24

Better for rare diseases

Retrospective case controls are quick and cheap

Question 25

What are the disadvantages of a case control study?

Answer 25

Prone to bias

Time of first exposure to risk factor is difficult to judge

Incidence can’t be determined

Question 26

What are the advantages of a cohort study?

Answer 26

Better for rare exposures

View the multiple effects of one exposure

Less prone to bias

Incidence can be determined

Question 27

What are the disadvantages of a cohort study?

Answer 27

Can be slow and expensive

Question 28

What are the two types of random errors?

Answer 28

Type 1 = alpha error

Type 2 = beta error

Question 29

What is a type 1 error?

Answer 29

A false positive

Question 30

What is a type 2 error?

Answer 30

A false negative

Question 31

How can type 1 errors be controlled?

Answer 31

By lowering the statistical significance level

Question 32

How can type 2 errors be controlled?

Answer 32

Increase sample size and power of the study

Question 33

What is sensitivity?

Answer 33

Measurement of how good a test is at diagnosing disease?
i.e. true positive rate

A high sensitivity reduced type 2 error

Question 34

What is specificity?

Answer 34

Measurement of how good a test is at diagnosing no disease?
i.e. true negative rate

High specificity reduces type 1 errors

Question 35

What is the formula for relative risk?

Answer 35

(Absolute risk when exposed) / (absolute risk when non-exposed)

i.e. [De / (De + He)] / [De’ / (De’ + He’)]

Question 36

What is the formula for odds ratio?

Answer 36

Odds of exposed / Odds of non-exposed

i.e. (De / He) / (De’ / He’) = (De He’) / (He De’)