Case Control Study Design Chapter 10

Question 0

List the titles for columns and rows in a 2 x 2 breakdown and how to assess the portion of exposed for case-control studies

Answer 0

Columns from left to right disease cases, no disease controls

Rows: from top to bottom exposed (those who ate chili peppers), non-expose (those who did not eat chili peppers)

Portions of the population who were exposed calculations are done from top to bottom in a column fashion

Example a/A+ c

Question 1

List the order of events for case-control studies

Answer 1

Select two groups of individuals: those with the disease (cases) and those that do not have the disease (controls)

And ascertain exposure

Determine the portion of exposed among the cases and the portion of non-exposed him on the cases. Determine a portion of exposed him on the controls and a portion of non-exposed among the controls

The portion of cases who were exposed is compared with the portion of Controls who were exposed

Question 2

Define measures of association

Answer 2

The chance of something happening that can be expressed as a risk or the odds

Question 3

Define risk

Answer 3

Risk equals the chance of something happening divided by the chances of all things happening

Question 4

Define odds

Answer 4

The chance of something happening divided by the chances of it not happening

Question 5

If the probability of something happening = 1/34 = 0.29

What are the odds

Answer 5

Formula = probability divided it by (1 -probability)

So 0.29/0.71= 0.41

Question 6

Give the formula for calculating odds ratio in a case control study

Answer 6

The odds of exposure among the cases/the odds of exposure among the controls

Or easy way:

The cross product ratio

A times D/B times C

Question 7

How are the odds ratios expressed when explaining the results

PAY ATTENTION TO THIS THIS WILL BE ON THE EXAM

Answer 7

The odds of being EXPOSED to chili peppers are 5.92 times greater for gastric cancer cases as compared to controls

Question 8

Interpretation of odds ratio (OR) as a measure of association in case-control studies

Answer 8

Exactly the same as cohort

OR = 1
Odds of exposure in the case is equal to the odds of exposure in the controls (no Association)

OR>1
Odds of exposure in the cases is greater than the odds of exposure in the controls (positive association)

OR<1
Odds of exposure in the cases is less then the odds of exposure and controls (negative association) protective effect

Question 9

Explain the relationship between OR and RR

KNOW THIS

Answer 9

OR ~RR: when the disease is RARE

CAUTION: OR > RR WHEN THE OUTCOME IS NOT rare

This can be explained because
O= p/1-p when P (risk of diseases small), then O=p/1

Question 10

Explain the process and reasoning of matching

KNOW THIS

Answer 10

Matching cases and controls-The process of selecting the control so that they are similar to the cases

This is done because we want the cases that controls to come from a similar population of except for the exposure were studying

Cases of controls me different certain characteristics (other than exposure) which may influence the outcome. Can control for this in the analysis or by matching

Question 11

List the problems with matching

Answer 11

If you match on too many characteristics it may be difficult to identify an appropriate control

If you match on a given characteristic then you can no longer study that characteristic

Never match on your EXPOSURE variable

Question 12

When analyzing a matched case-control study what parts of the 2 x 2 are used and why

KNOW

Answer 12

B/C

We do not compare a and D because they are matched and they won’t teach you anything

Expressed in sentence form as:

Uterine cases were three times more likely to be exposed to estrogen then MATCHED controls

Question 13

What are the necessary elements for case selection in a match case control study

Answer 13

Establish a case definition and stick with it (strict diagnostic criteria)

Cases can be new cases (incidents) or existing (prevalence) cases

Cases must be representative of persons with the disease in a population

Identify the sources of your cases:

Hospitals

Public health clinics

Physicians offices

Disease registries

Question 14

Explain the necessary steps for control selection in matched case controlled studies

Answer 14

Selection of an appropriate comparison group is the most difficult and critical issue in the design of case control study

Controls our subjects FREE of the disease (or outcomes of interest)

Control should come from the same source population is the cases

The prevalence of exposure of the control should be similar to the prevalence of exposure among the source population

Source of control:

General population

Random digit dialing

Friends relatives

Hospital or clinic-based

Question 15

Advantages and disadvantages of using general population as controls

Answer 15

Advantages

Represent the population from which the cases were selected

Disadvantages

Costly and time-consuming

How to identify people in the population

Hard to contact people

Poor recall than hospital controls

Less motivated to participate then other controls

Question 16

Advantages and disadvantages of random digit dialing for controls

Answer 16

Advantages

May approximate random sample from the source population. Controls are often match to cases on area code and prefix

Disadvantage

Possibility of contacting each eligible subject may differ due to time of day, number and household, color ID

Widespread cellular-phone used to reduce his value

Question 17

Advantages and disadvantages of friend and relative controls

Answer 17

Advantages

Healthier than hospital controls

Tend to be more could a whopper lived in general population controls

Often similar cases on factors such as SES, lifestyle, and ethnic background

Disadvantages the list of potential friends/relatives control is often derived from the case, this dependence May add a potential source of bias

Friend relative controls may be TOO similar to cases regarding the exposure of interest

Question 18

Advantages and disadvantages of hospital controls

Answer 18

Advantages

Easily identified, sufficient number, low-cost

More likely to cooperate, minimize nonresponse bias

Hospital selection factors that influence decision to come to a particular hospital maybe similar to cases

May be more aware of past exposures at events

Disadvantages

Differ from healthy people, may not represent the exposure distribution of the population where the cases were obtained

Controls should be limited to diagnoses for which there are no prior indications of a relationship with exposure

Question 19

How many controls per case

Answer 19

The optimal case-control ratio is 1 to 1

When the number of cases is small the sampling size for the study can be increased by using more than one control case

Question 20

List the criteria for accessing exposure for those that occurred before the onset of disease

Answer 20

Study subjects-self reporting questionnaires

Particularly vulnerable to recall bias as cases may recall their exposure history more thoroughly than controls

Existing records (completed before the occurrence of outcome events)

Work history-industrial hygiene

Hospital-birth, diagnostic

Prescriptions

Interviews with Sarah get (spouse a sibling)

Question 21

Advantages to case-control studies

Answer 21

Relatively quick and inexpensive

Small sample sizes

Optimal for evaluation of RARE DISEASES

can examine multiple etiologic factors for a single disease

Question 22

Disadvantages to case-control studies

Answer 22

Inefficient for evaluation of rare exposures unless the disease is common among the expose

Disease status can influence the selection of the case and control subjects

Maybe difficult to establish the temporal relationship between exposure and disease. Exposure measurements are collected after disease occurrence

Prone bias compared to other analytical study designs, in particular selection and recall bias

Question 23

Explain nested case-control studies

Answer 23

Occur after the establishment of a cohort study

Identify cases as they develop

Choose controls as the case is selected or at random

Question 24

Advantages of nested case-control studies

Answer 24

Decrease in recall bias-dad and I are obtained before the disease develops

Identify risk factors, rather than early or subclinical disease as the specimens were obtained years before disease occurs

Less expensive to conduct (only if someone has already initiated the cohort)

Increased comparability between cases and controls