Epidemiology Study designs

Cohort (Follow-Up) Studies consists of what two types of studies

Prospective and Retrospective (Historical) Studies

Cohort Studies

Start With Exposed Group followed over a long period of time to determine disease status

Calculating the incidents rate

Prospective Cohort Studies

Starts with present and collects into the future

Follow-up over long periods of time to see how disease has developed

Retrospective Cohort Studies

Data has already been collected in the past

Used to study Occupational or Environmental exposures

Look at current health records to see who developed the disease

Advantages of Prospective Cohort Studies

1. Can determine incidence

2. Good for Rare Exposures

3. Can study multiple Outcomes

Disadvantages of Prospective Cohort Studies

1. Long period of Follow-up

2. Time Consuming

3. Expensive

Advantages of Retrospective Cohort Study

1. No long follow up period (disease already occurred)

2. Less expensive

3. No problems with non-participation

Disadvantages of Retrospective Cohort Study

1. Large number of subjects

2. Expensive

3. Tracking can be Time Consuming

Case-control

1. Has cases and controls

2. Identifies potential exposures back in time

3. Measures odds ratio

Case Control Advantages

1.Short/No period of Follow-up

2. Smaller number of subjects

3. Good for studying rare Diseases or those of long latency

4. Less time consuming, Less Expensive

Case control Disadvantages

1. Selection bias

2. Interviewer Bias

3. Less certain of exposure status

Clinical Trials

The investigators influence the exposure of the study subjects

Randomization and Blinding occurs

Field Trials

Community Trials

Advantages of clinical trials

1. Fewer Biases

2. Gold Standard

3. Control for unknown factors

Disadvantages of Clinical Trials

1. Complex Design

2. Expensive

3. Time Consuming

Cross-Sectional Studies

Designed to determine what is happening right now

Disease and exposure status are determined at the same time

Usually uses surveys and polls

Advantages of Cross-Sectional Studies

1. Inexpensive

2. No loss to follow-up

3. Used for public health planning

Disadvantages of Cross-Sectional

1. Only a snapshot

2. Can only determine prevalence

3. No information on cause-effect relationship

Prevalence Formula

PE=A/A+B PnE=C/C+D (Cross-Sectional)

Incidents Rate Formula

IE= A/A+B InE=C/C+D (Cohort Study, Clinical Trials)

Odds Ratio

Odds of Exposure D= A/C

Odds of Exposure ND=B/D

OR=AD/BC (Case Control)