1 - Case Control, and Longitudinal Cohort Studies

Question 1

Sample

Answer 1

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

Question 2

Cause

Answer 2

Exposure or Intervention

Question 3

Effect

Answer 3

Disease or Outcome

Question 4

2 x 2 table - A

Answer 4

Exposed + Outcome

Question 5

2 x 2 table - B

Answer 5

Exposed + No Outcome

Question 6

2 x 2 table - C

Answer 6

Not Exposed + Outcome

Question 7

2 x 2 table - D

Answer 7

Not Exposed + No Outcome

Question 8

Prospective Study

Answer 8

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

Question 9

Ideal Experiment for Cause/Effect

Answer 9

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

Question 10

Interventional Studies

Answer 10

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

Question 11

What can’t we examine with interventional trials?

Answer 11

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

Question 12

Observational Studies

Answer 12

Cohort or Case Control

Question 13

Cohort Study Types

Answer 13

Longitudinal (prospective, going forward, retrospective

Question 14

Cohort Study

Answer 14

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.

Question 15

Pros of a Cohort Study

Answer 15

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

Question 16

Cons of a Cohort study

Answer 16

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?

Question 17

Measuring the effect of a Cohort Study - Questions

Answer 17

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

Question 18

Risk of Disease (in Exposed)

Answer 18

(Exposed & Diseased)/(Total Exposed)

Question 19

Risk of Disease (in Unexposed)

Answer 19

(Unexposed & Diseased)/(Total Unexposed)

Question 20

Critiquing a Cohort Study - Questions

Answer 20

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?

Question 21

Tools to determine how meaningful results of a cohort study are

Answer 21

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

Question 22

Absolute Risk

Answer 22

AMOUNT of disease in the population

Question 23

Relative Risk (Risk Ratio)

Answer 23

(Risk in Exposed)/(Risk in Unexposed)

Question 24

RR = 1

Answer 24

There is no association of exposure to disease

Question 25

RR

Answer 25

The exposure is protective against the outcome

Question 26

RR > 1

Answer 26

The exposure is associated with the outcome

Question 27

Attributable Risk (Risk Difference or Absolute Risk Increase)

Answer 27

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

Question 28

Attributable Risk Formula

Answer 28

Risk in Exposed - Risk in Unexposed

Question 29

Number Needed to Harm

Answer 29

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

Question 30

Number Needed to Harm Formula

Answer 30

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

Question 31

Problems with the Cohort Study

Answer 31

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?

Question 32

Confounding Factor

Answer 32

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

Question 33

Bias

Answer 33

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

Question 34

How do we control for confounding factors?

Answer 34

Stratification

Question 35

Stratification

Answer 35

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

Question 36

Regression

Answer 36

Controlling for many possible confounders at the same time.

Question 37

Selection Bias

Answer 37

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

Question 38

Loss to Follow Up Bias (Attrition)

Answer 38

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

Question 39

Limitations to Cohort Studies

Answer 39

``` 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 ```

Question 40

Positives of a Cohort Study

Answer 40

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)

Question 41

When do we use a Case-Control Study?

Answer 41

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

Question 42

Case-Control Study

Answer 42

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

Question 43

Pros of a Case-Control Study

Answer 43

Quicker analysis | Fewer people required

Question 44

Difficult part of Case-Control

Answer 44

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?)

Question 45

Case-Control Process - Were they exposed?

Answer 45

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

Question 46

Case Control - Measure of Association

Answer 46

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

Question 47

Odds that a case was exposed

Answer 47

Exposed Cases / Unexposed Cases

Question 48

Odds that a control was exposed

Answer 48

Exposed Controls / Unexposed Controles

Question 49

Odds Ratio

Answer 49

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

Question 50

OR = 1

Answer 50

No effect of the exposure on disease

Question 51

OR > 1

Answer 51

The exposure has an association with disease

Question 52

OR

Answer 52

The exposure is protective against disease

Question 53

Problems with Case Control

Answer 53

Disease already exists | Have to look back and rely on memory/records

Question 54

Bias in Case Control

Answer 54

Recall Bias | Selection Bias

Question 55

Recall Bias

Answer 55

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

Question 56

Selection Bias

Answer 56

How controls are chosen compared to the cases

Question 57

Prescription Bias

Answer 57

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

Question 58

When can Odds estimate Risk

Answer 58

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

Question 59

Cross-Sectional Study

Answer 59

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