Study Design Definitions

Question 1

Cross-Sectional Study Design

Answer 1

A way to establish prevalence of disease in a population by simultaneously collecting data on exposure and disease at one single point in time.

Question 2

Ecological Study Design (Correlation Study)

Answer 2

Collecting group (aggregate) or averages data. This is a study of group characteristics.

Question 3

Case Control Studies

Answer 3

This type of study is used to identify whether an exposure has resulted in the development of a disease. Investigator compares cases with controls. Investigator will ask individuals in both groups about their exposure.

Question 4

Prospective Cohort Study Design

Answer 4

Describes relationship between exposure status at start of study and development of outcome over time.

Most powerful type of observational study design

Question 5

Retrospective Cohort Study Design

Answer 5

Starts with people who already have the disease and looks back in time at the exposures to determine the cause.

Question 6

What to look for in an ecologic study

Answer 6

Unit of observation: Groups/Communities/Population level

Assessment: Correlation between exposure rates and disease rates among groups or populations.

Use of aggregate data or group averages

Ex: Breast cancer incidence in countries compared to level of fruit/veggie intake in country

Question 7

What are the advantages of ecologic studies?

Answer 7

1. Helps us understand group exposures (environmental)
2. Allows us to distinguish exposures between groups rather than within
3. Helps with identifying a problem or generating a hypothesis
4. Data is already collected so it’s inexpensive!
5. Looking for prevalence

Question 8

What type of study is an ecologic study?

Answer 8

Analytic

Question 9

What are the disadvantages of an ecologic study?

Answer 9

1. Groups can have more differences than just the type of exposure
2. Group level data varies in quality.
3. Investigator can introduce error into results by including only some groups but not others.
4. Ecological Fallacy: people with the outcome may not be the ones with the exposure.

Question 10

Study Group: 14 countries (school-aged children)
Exposure: Meteorological Variables (environment factors)
Outcome: Prevalence of asthma

Answer 10

Ecological Study Design

Question 11

Cross-Sectional Study Design (Prevalence Study)

Answer 11

Viewing a the prevalence of disease in a population at a certain time. A snapshot!
1. Measure the levels of serum cholesterol levels in a surveyed population
2. Perform an ECG for evidence of CHD
3. Presence of CHD=prevalent case

Question 12

Cross-Sectional Study Limitations

Answer 12

1. Can’t establish temporality because we only know prevalence of a disease in a population at a certain timepoint. We don’t know when it developed.
2. Selection Bias: Only identifying prevalent cases excludes those those who died sooner after the disease developed, but before study was carried out.

Question 13

Prevalent cases=

Answer 13

Survivors

Question 14

What study designs measure prevalence?

Answer 14

Ecologic, Cross-Sectional