Study design

Question 1

What are the types of studies?

Answer 1

Descriptive
Migrant 
Analytical Epidmiology - cross-sectional, case-control, cohort
Experimental
In vitro lab studies

Question 2

Define bias

Answer 2

estimate of systematic measurement error

Question 3

What are the types of bias?

Answer 3

Selection bias
Information bias
Prevalence bias

Question 4

Define selection bias

Answer 4

bias because of errors in selection of study population or selective loss-to-follow up

Question 5

Define information bias

Answer 5

bias because of errors in the measurement of exposure or the disease outcome

Question 6

Define prevalence bias

Answer 6

slowly progressing cases are more likely to be sampled in a cross-sectional survey than those with severe/faster disease progression

Question 7

Define counding

Answer 7

Mixing of the effects of exposure on the outcome with the effects of a third variable

Question 8

When is a factor a confounder?

Answer 8

Affects risk of the studied health outcome
Associated with the exposure of interest
Not an intermediate in the causal chain between the exposure of interest and the health outcome

Question 9

What is mediation?

Answer 9

factor that is associated with the exposure of interest and the disease outcome and lies on the causal pathway

Question 10

Give an example of exposure, outcome and confounder

Answer 10

Exposure = Controlling mothers
Outcome = High fat/ Low fat
Confounder = Academic focus will lead to more controlling mothers and it lead to high fat/ low fat intake cuz kids are stressed
Not a confounder = gene ->high fat/low fat but no association with exposure

Question 11

Give an example of mediation

Answer 11

Exposure = Dairy
Outcome = Hip fractures
Mediation = Calcium
Dairy causes hip fractures through calcium

Question 12

What is the bias in this example?
Case: persons with pancreatic cancer identified through hospitals
Controls: persons without pancreatic cancers identified through the same physicians as the cases
Result: coffee consumption associated with pancreatic cancer

Answer 12

Selection bias. Controls did not have coffee consumption habits representative of the source population / diet not reflective of population as a whole

Question 13

What is the bias in this example?
Case: women with asthma
Controls: women without asthma with the same family doctor
Result: lower fruit consumption is associated with asthma

Answer 13

Selection bias. Controls that responded may have been a very motivated, health conscious selection with higher fruit consumption than source population

Question 14

What is the bias in this example?
Case: women with breast cancer
Controls: women without breast cancer
Result: higher fat intake was associated with higher risk breast cancer

Answer 14

Recall bias. Women with breast cancer may have over-estimated their past fat- intake. They might think why they have breast cancer and not others? then they think its their consumption of fat

Question 15

What are case reports?

Answer 15

description of rare clinical events
Highly detailed, can use sophisticated methods
Unable to estimate frequency or the role of bias or chance

Question 16

What are case series?

Answer 16

study of a larger group of patients witha particular health condition
limitation: absence of comparison group

Question 17

What is an ecological study?

Answer 17

Observational studies in which the unit of analysis is a group rather than an individual. (usually used for making hypothesis, rather than causal effect)

Question 18

What are the limitations of an ecological study?

Answer 18

Many differences that are difficult to disentangle (confounders)
Ecological fallacy - inferences about individuals based on group level data

Question 19

Device a randomised controlled trial

Answer 19

population - group 1 - treatment - outcome
-group 2 - control - outcome

difference is just treatment given or not given

Question 20

What are the potential limitations of randomised controlled trial?

Answer 20

cannot blind people cuz nuts is not a type of drug that can be disguised

Compliance
Ethical issues
Generalisability
High cost and long duration

Question 21

Device a cohort study

Answer 21

Population - disease free - unexposed (D or ND)
-exposed (D or ND)

look at population through time (forward)

Question 22

Evaluate a cohort study

Answer 22

exposure assessed before disease diagnosis which reduces selection and recall bias

Limitations: residual confounding and loss-to-follow up can be potential problems

May not be feasible with rare diseases and exposure-diseaase relationships with long induction period

Question 23

what is the difference between case-control and cohort study?

Answer 23

cohort study: selection of disease-free population and then categorising them into exposure and non-exposure group them do a follow-up to see who developed the disease and who did not

case-ctrl: selection based on outcome (case vs controls) and then look into past and compare exposure

Question 24

What is a case-control study?

Answer 24

comparison of the frequency of exposure between cases and controls

selection of incident cases within a specific period of recruitment

selection controls: from comparable population without the disease (eg community, other hospitals)

Question 25

What are the limitations of case-control study?

Answer 25

prone to recall and selection bias as comparedd to cohort study

Question 26

What are the advantages of cross-sectional studies?

Answer 26

Advantages:
fairly simple, rapid and inexpensive
can study a wide range of factors

Disadvantages:
not good for rare diseases (prevalence of chicken pox)
reverse causation: “chicken or egg”
length bias

Question 27

Interpretation of results?

Answer 27

was the finding due to bias?
was the finding due to chance?
was the finding due to confounding?