Case control study (Review of an Article)

CASE CONTROL STUDY

Submitted by :- Baldev Singh

INTRODUCTION

A study that compare two groups of people, those with the disease

or condition under study (case) and a very similar group of people

who do not have the disease or condition (controls).

Essential elements

Both exposure and disease have occurred

Proceeds from effects to cause

Uses a comparison ‘control’ group.

PRINCIPLE OF CASE

CONTROL STUDY

Assemble

cases disease

Assemble

controls not

having disease

Measure

exposure

status

Exposed and

non-exposed

Time

Direction of Enquiry

DESI GN OF CASE –CONTROL STUDY

ExposeNon-

Expose

Disease Non-Disease

ExposeNon-

Expose

Cases Controls

2X2 TABLE

Disease Non- Disease Total

Exposed A B A+B

Non-exposed C D C+D

Total A+C B+D A+B+C+D

STEPS IN CASE CONTROL

Selecting of cases and controls.

Matching.

Measurement of exposure.

Analysis and interpretation.

S E L E C T I O N O F C A S E S A N D C O N T R O L S

Define case – Diagnostic and eligibility criteria.

Sources of cases- Hospital, General population.

Define control – Free from disease

Sources of Control – Hospital, Relatives, Neighborhood controls,

General population.

Number of controls.

MATCHING

Ensure comparability between cases and controls

A confounding factor is defined as one which is associated both

with exposure and disease, and is distributed unequally in study and

control groups.

Suspected etiological factor should not be matched

Types of matching : Pair, Frequency

MEASURE THE EXPOSURE

Define exposure-

Measure in precisely the same manner both for cases and controls

ANALYSIS

Exposure rate among cases and controls

Odds Ratio – AD/BC (also called cross product ratio)

Example: Depression and Vegetable eating

Individuals with

depression (cases)

Individuals without

depression (controls)

Total

Eat Vegetables 90 90 180

Do not eat

Vegetables

130 130 260

Tatal 220 220 440

ANALYSIS..

Odds of exposure among cases : A/C = 90/130 = 0.6923

Odds of exposure among controls : B/D = 90/130 = 0.6923

Odds Ratio = 0.6923/0.6923 =1.0

BIASES

Memory or recall bias

Selection bias

Interviewer bias

Bias due to confounders

ADVANTAGES & DISADVANTAGES

Advantages Disadvantages

Easy to carry out Subject to several biases

Rapid results Selection of controls difficult

Inexpensive Incidence can’t be measured

Suitable for rare diseases Association doesn’t mean causation

No risk to subjects Not practical for rare exposure

Minimal attrition

Multiple exposures can be studied

ARTICLE REVIEW

A Case-Control Study of

Drinking Habits Past and Present

Authors

Helen Rodgers, MRCP; Philip D. Aitken, FRACP; Joyce M. French, BSc;

Richard H. Curless, MRCP; David Bates, FRCP; Oliver F.W. James, FRCP

I NTRODUCTI ON OF THE STUDY

Background and Purpose: Previous studies have reported a U-shaped

relation between alcohol consumption and stroke. Those studies have been

criticized for failing to distinguish between lifelong abstainers from alcohol

and those who have given up drinking.

Objective : The contribution of alcohol to the risk of stroke

in moderate and heavy drinkers, lifelong abstainers and current

abstainers using validated measures of alcohol consumption.

Methods: They examined current and previous drinking habits of 364 cases

of acute stroke and 364 community-based control subjects matched for age,

sex, and family practitioner.

I NTRODUCTI ON OF THE STUDY

Results: Stroke patients were more likely to have been lifelong

abstainers from alcohol than were the control subjects. The odds

ratio (OR) of lifelong abstainers versus those who had ever drunk

regularly was 2.36 (95% confidence interval [CI], 1.67 to 3.37). No

relation was found between stroke and current nondrinkers. Current

male heavy drinkers also had an increased risk of stroke (OR, 2.88;

95% CI, 1.08 to 2.31).

Conclusions:……………….

SUMMARY

CRITIQUES

Positive :

I. This study shows the well established relationship between alcohol

consumption and strokes.

II. The study show not only the relationship between alcohol

consumption & strokes, but also show the relation with other disease

like hypertension, cerebral infarction etc.

Negatives :

I. Cases of the study is only from the hospital record, while controls are

taken from community.

II. Study does not described clearly about the hypertension and cerebral

infarction.

CONCLUSION & REFRENCE

Conclusion

Lifelong abstention from alcohol is associated with an increased

risk of stroke. Moderate alcohol consumption may protect against

cerebrovascular disease.