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FCM - Evidence Based Medicine > 1 - Case Control, and Longitudinal Cohort Studies > Flashcards

1 - Case Control, and Longitudinal Cohort Studies Flashcards

1
Q

Sample

A

The subset of the population that is chosen to be in the study

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2
Q

Cause

A

Exposure or Intervention

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3
Q

Effect

A

Disease or Outcome

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4
Q

2 x 2 table - A

A

Exposed + Outcome

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5
Q

2 x 2 table - B

A

Exposed + No Outcome

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6
Q

2 x 2 table - C

A

Not Exposed + Outcome

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7
Q

2 x 2 table - D

A

Not Exposed + No Outcome

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8
Q

Prospective Study

A

At the beginning, nobody has the outcome. Exposure happens, outcome happens. Cause is proven.

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9
Q

Ideal Experiment for Cause/Effect

A

All start out unexposed
Sample accurately reflects population
Random assignment to exposed/unexposed groups
None have the outcome at the beginning (prospective)
Outcome happens quickly and not rarely.
Exposure and outcome are not harmful

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10
Q

Interventional Studies

A

Researchers DO something to exposure group
Sample requires subjects/volunteers
First Step - Exclusion Criteria (Limit # of other causes, but may not reflect population)
Second Step - Randomization
Third Step - Test and monitor for some period of time
Result - Applicability to real life patients is limited

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11
Q

What can’t we examine with interventional trials?

A 
Physiologic Phenomenon
Social/Environmental Phenomenon
Exposure is harmful, unethical
Outcome is rare
Outcome happens a lont time after exposure
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12
Q

Observational Studies

A

Cohort or Case Control

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13
Q

Cohort Study Types

A

Longitudinal (prospective, going forward, retrospective

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14
Q

Cohort Study

A

Start with exposure (selected/sampled based on their exposure)
Start without outcome
Groups “CHOOSE” what groups they are in. This means we see the effects of other exposures that “come with” the exposure in question. We must measure the confounding exposures.

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15
Q

Pros of a Cohort Study

A

Prospective (stronger relationship between cause & effect)
Real life populations
Multiple out comes can be studied

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16
Q

Cons of a Cohort study

A

People choose their own groups (lots of things “come with” the exposure)
Following people for a long time, lose people
Are people in one group more likely to drop out than others?

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17
Q

Measuring the effect of a Cohort Study - Questions

A

Is there a cause and effect relationship?
Use a Measure of Association
Cohort Studies - Risk

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18
Q

Risk of Disease (in Exposed)

A

(Exposed & Diseased)/(Total Exposed)

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19
Q

Risk of Disease (in Unexposed)

A

(Unexposed & Diseased)/(Total Unexposed)

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20
Q

Critiquing a Cohort Study - Questions

A

Is this amount clinically meaningful?
Could this difference be due to chance?
Could there have been other reasons that the exposed group had more outcomes?

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21
Q

Tools to determine how meaningful results of a cohort study are

A

Absolute Risk
Relative Risk (Risk Ratio)
Population Attributable Risk (Risk Difference)
Number Needed to Harm, Number Needed to Treat

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22
Q

Absolute Risk

A

AMOUNT of disease in the population

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23
Q

Relative Risk (Risk Ratio)

A

(Risk in Exposed)/(Risk in Unexposed)

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24
Q

RR = 1

A

There is no association of exposure to disease

25
Q

RR

A

The exposure is protective against the outcome

26
Q

RR > 1

A

The exposure is associated with the outcome

27
Q

Attributable Risk (Risk Difference or Absolute Risk Increase)

A

The amount of the disease in the population that is “attributable” to the exposure

28
Q

Attributable Risk Formula

A

Risk in Exposed - Risk in Unexposed

29
Q

Number Needed to Harm

A

How many people would have to be exposed for 1 person to develop disease

30
Q

Number Needed to Harm Formula

A

1/(Attributable Risk)

=1/(Risk in Exposed - Risk in Unexposed)

31
Q

Problems with the Cohort Study

A

What else might “come with” exposure?
Who did we include in the study? What “comes with” our selection methods?
Who stayed in the study for the whole year?

32
Q

Confounding Factor

A

Another factor that “comes with” the exposure and affects the outcome.
Can be controlled for

33
Q

Bias

A

Problems with the structure of the study that affect who participates, how we measure, or how we analyze.
Can’t be controlled for

34
Q

How do we control for confounding factors?

A

Stratification

35
Q

Stratification

A

Separate out results into categories by confounding factors, see if there’s a difference.

36
Q

Regression

A

Controlling for many possible confounders at the same time.

37
Q

Selection Bias

A

Do we choose people in the exposed/unexposed differently and in a way that could be associated with the outcome?

38
Q

Loss to Follow Up Bias (Attrition)

A

If people are less likely to stay in the study based on their exposure status, it can affect results

39
Q

Limitations to Cohort Studies

A 
Require a lot of people
Require a long time
Require a lot of money
Need to have some idea there is an association before investing in it
Very prone to confounding
40
Q

Positives of a Cohort Study

A

Can study exposures that can’t be “done to” people
Can study multiple different kinds of outcome from an exposure
Can calculate RISK because exposure clearly came before outcome (prospective)

41
Q

When do we use a Case-Control Study?

A

When a disease is RARE or takes a LONG TIME to develop (Cancers, etc)

42
Q

Case-Control Study

A

Retrospective
Start with a group of people with the disease, and a group without the disease.
Look back to see if they had the exposure

43
Q

Pros of a Case-Control Study

A

Quicker analysis

Fewer people required

44
Q

Difficult part of Case-Control

A

Choosing Controls
Attempt to limit Bias and Confounding
Matching (by individual or by group)
Where do cases vs. controls come from? (Cases come from hospital/medical setting, does this generate bias or confounding?)

45
Q

Case-Control Process - Were they exposed?

A

Collect data from past exposures (Medical records - was it recorded? Interviews - Memory?)
Needs to be at a point in time BEFORE DISEASE

46
Q

Case Control - Measure of Association

A

Disease already exists, does not have temporal relationship of cause - effect
Can’t calculate risk
Can only calculate odds

47
Q

Odds that a case was exposed

A

Exposed Cases / Unexposed Cases

48
Q

Odds that a control was exposed

A

Exposed Controls / Unexposed Controles

49
Q

Odds Ratio

A

(Exposed Cases x Unexposed Controls) / (Unexposed Cases x Exposed Controls)

50
Q

OR = 1

A

No effect of the exposure on disease

51
Q

OR > 1

A

The exposure has an association with disease

52
Q

OR

A

The exposure is protective against disease

53
Q

Problems with Case Control

A

Disease already exists

Have to look back and rely on memory/records

54
Q

Bias in Case Control

A

Recall Bias

Selection Bias

55
Q

Recall Bias

A

Those with disease are more likely to recall exposures than those without disease

56
Q

Selection Bias

A

How controls are chosen compared to the cases

57
Q

Prescription Bias

A

Confounding by Indication
For studies involving medications, the decision to give a certain medication can be affected by other factors that also affect the outcome

58
Q

When can Odds estimate Risk

A

If disease is rare (less than 20% of population has the disease)
AND
The sample for the study is an unbiased representation of the population

59
Q

Cross-Sectional Study

A

“Prevalence Study”
Define a population
Gather data on presence/absence of exposure and disease at that time for each individual.
Snapshot

FCM - Evidence Based Medicine (11 decks)

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