Case control studies Flashcards

1
Q

What are GWAS

A

genome wide association studies

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2
Q

What is are Bradford - Hill criteria

A

minimum conditions necessary to provide adequate evidence of a causal relationship between incidence and outcome

1 strength of assoc
2 consistency (of study designs, populations)
3 specificity
4 temporality
5 dose response relationship
6 biological plausibility
7 coherence
8 experimental evidence
9 analogy (alternative explanations)
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3
Q

Why might there be inconsistencies between reports of associations between genotype and outcome?

A

Variation of underlying associations in populations (different ethnicities have different variants of genes which can effect outcome)

Heterogenous phenotype

confounding factors

chance

publication bias

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4
Q

What are the advantages/disadvantages of a case control study

A

inexpensive and quick
good for quick outcomes

not good for rare exposures
prone to selection recall bias
no estimates for disease incidence

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5
Q

Why should controls in a study come from the same population as the cases?

A

Same confounding factors; reduces differences in risk factors between groups

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6
Q

How do you calculate odds ratio

A

Ratio of disease odds in exposed group to disease odds in unexposed group

say for smokers and cancer

(smokers who develop cancer / smokers who don’t) / (non smokers who develop cancer / non smokers who don’t)

Shows that someone who has cancer is 2.25x more likely to be a smoker

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7
Q

Why is selection bias of controls important

A

Different groups have different incidence rates for diseases.
Say if you were going to use a hospital ward as the control group for a trial - the ward you pick will have different incidences of diseases from a different ward (e.g trauma ward vs non-trauma ward)

So this affects odds ratio in final result

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8
Q

What is diagnostic bias and what effect can it have

A

where a treatment process leads to an increased detection of the disease (like people on birthcontrol dont get periods, so when they bleed it is a sign of cancer - but if she wasnt on the birthcontrol the bleeding wouldnt necessarily be considered abnormal so the cancer wouldn’t be detected) so this leads to an INCREASE IN OR

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9
Q

What is survival bias

A

Only patients who have survived a lethal disease can enter the study DECREASE IN OR

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10
Q

What is admission bias

A

exposed cases more likely to be admitted than controls INCREASE IN OR

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11
Q

What is non-response bias

A

people not taking treatment/test (e.g not turning up to a scan) DECREASE IN OR

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12
Q

What is recall bias

A

people in exposed group remember events better than controls INCREASE IN OR

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13
Q

What is interviewer bias

A

different questions asked to either group

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