Population and Social Science

Question 1

Name the 4 types of observational studies.

Answer 1

• Descriptive
  
  • Cross-sectional
  • Ecological
• Analytical
  
  • Case-control
  • Cohort

Question 2

Describe how an ecological study is conducted.

Answer 2

• Population level (group analysis)
• Observational
• Ecological fallacy (inference made about individuals from group data collected)

(Ecological fallacy= type of confounding variable)

Question 3

Describe a cross-sectional survey/study.

Answer 3

• Measures exosure and disease- one point in time
• Data from individuals

Question 4

Define prevalence and incidence rate.

Answer 4

Prevalence: Existing cases as proportion of population

Incidence rate: New cases in population per year (Person-years)

Question 5

What can prevalence and incidence rate be used to measure?

Answer 5

Absolute risk (of event happening)

Question 6

What is an incidence rate ratio?

Answer 6

Compares incidence rate of 2 populations

Is exposure associated with condition?

Question 7

What is the difference between incidence rate ratio and risk ratio?

Answer 7

Incidence rate ratio= incidence rate

Risk ratio= prevalence

Question 8

Identify a solution to limit the effect of confounding variables in a study.

Answer 8

1. Selection (match confounders)
2. Calculations (standardisation, stratifying etc)

Question 9

What is the standardised mortality ratio?

Answer 9

SMR: Observed/expected deaths x 100

Question 10

What does a SMR> 100 suggest?

Answer 10

Excess mortality with confounders accounted for

Question 11

When measuring mortality rate, what’s the difference between direct and indirect standardisation?

Answer 11

Direct= uses reference population (same population numbers)

Indirect= uses mortality rates from one population to another (observed and expected deaths)

Question 12

What is the sampling frame?

Answer 12

List or method through which sample= obtained

(assumed to be representative of population)

Question 13

Why do we use an Error Factor (EF) with epedimiological studies?

Answer 13

• True value of population= different to sample
• Error factor used to help infer true value
• Size of EF depends on size of population

Question 14

What is the confidence interval?

(Use EF to work out CI)

Answer 14

Interval where the true value lies

(which we can say with 95% confidence)

Question 15

What are the 2 types of validity a study must have?

Answer 15

1. Internal validity
   
   1. Freedom from confounding, bias, random error
2. External validity
   
   1. Degree to which conclusions from study can be applied to population of interest

Question 16

Define bias.

Answer 16

Systematic error….

…measuring exposure/ covariates/outcome variables…

…leads to erroneous association

Question 17

What are the 2 main types of bias?

Answer 17

• Selection bias
• Information bias

Question 18

What is selection bias?

Answer 18

Selected sample not representative of patient population

Question 19

Why might selection bias occur?

Answer 19

• Systematic error selecting subjects
• Factors influencing participation

Question 20

How might information bias occur?

Answer 20

• Misclassification of participants
• Recall error/bias (case-control problem)
• Observer error/bias
• Measurement error/bias

Question 21

Describe how a cohort study is conducted?

Answer 21

1. Recruit disease-free individuals
2. Classify according to exposure
3. Follow - long periods of time
4. Monitor disease progress
5. Calculate incidence rates

Retrospective/prospective

Question 22

What are the advantages of cohort studies?

Answer 22

Good for:

• rare exposures (not good for rare outcomes)
• conditions fluctuating with age
• multiple outcomes
• showing exposure precedes outcomw

Question 23

What are the disadvantages of cohort studies?

Answer 23

• Resource intensive
• Take long time
• Survivor bias
• Difficult with unknown confounders

Question 24

How are case-control studies carried out?

Answer 24

• Recruit disease free and diseased individuals
• Determine exposure status of each group
• Produce odds ratio (measure of relative risk)

Question 25

How are controls found for case-control studies?

Answer 25

Found to match confounders eg age, sex Make 2 populations as **similar** as possible

Question 26

What can be done when conducting a case-control study to minimise the EF (error factor)?

Answer 26

Use more **controls** than **cases**

Question 27

Give some advantages of using a case-control study:

Answer 27

* Good- rare disease * Cheap * Quick * Can study multiple exposure for single outcome

Question 28

Give some disadvantages of using a case-control study:

Answer 28

* Prone to selection and information bias * Not good for rare exposures * Confounding

Question 29

Looking at the following table, how is the odds ratio calculated?

Answer 29

Question 30

Differentiate between cohort and case-control studies.

Answer 30

Question 31

What is the **Bradford-Hill criteria** and what is it used for?

Answer 31

* Assesses how sure we are of a **causal relationship** * Criteria: * Association * Exposure&Outcome * Other evidence

Question 32

Why are RCTs (randomised controlled trials) carried out?

Answer 32

To assess: * **Efficacy** (benefit of treatment under specified conditions) * **Safety** (not doing harm under specified conditions)

Question 33

RCTs(randomised controlled trials) must be reproducible (under same conditions). They must also be 2 other things- what are these?

Answer 33

1. Controlled 1. Comparison of intervention 2. Fair 1. Unbiased, no confoundin/g

Question 34

What 3 measures can be taken to ensure that randomised control trials (RCTs) are **reproducible**, **controlled** and **fair**?

Answer 34

1. Randomisation 1. Removes confounding and allocation bias 2. Blinding 1. Removes measurement bias and non-treatment effects 3. Placebo 1. (patients must be told if standard treatment available)