Review Module 3 key words for study designs (Public Health Surveillance)

Cross-sectional study

• Exposure and disease measures made at the individual level

• Exposure and disease status determined at the same time

• A “snapshot” of the study population

• Prevalence study

  • prevalence cases

Data collection methods for a cross-sectional study

• survey questionnaire (in person, mail, phone, online, mobile device, etc.)

• existing database (hospital discharge data, health insurance claims data)

  • CDC’s Behavioral Risk Factor Surveillance System

  • National Health and Nutrition Examination Survey

When would you use the cross-sectional study design

estimation of the magnitude and distribution of a health problem

• measures the prevalence

Cohort studies

• select/classify subjects based on the status of exposure

• follow over time to compare incidence of disease between the exposed and non-exposed

Prospective Cohort

Investigator collects information on the exposure status of study subjects at the time the study begins and identifies new cases of disease that develop from that time on, until the end of the follow-up interval

• looking forward in time

• period of follow-up occurs after the study is initiated

Retrospective cohort

• investigator determines exposure status from information recorded at some time in the past, and disease status is determined from that point in the past up until the present (i.e., the follow-up period has already occurred)

• looking back in time

• period of follow-up has already been completed before study starts

• reconstructing a cohort experience that has already happened

Explain the Framingham study

In 1948, more than 5000 men and women, free of CVD, were identified, and exposed and not exposed groups were defined according to the presence of smoking, obesity, high blood pressure, etc

• New CVD was identified by examining the study population every 2 years over a 20-year follow-up period

Choice of Cohort Study Design

• Good design to study rare exposure

• More certain of temporal relationship between exposure and disease

• Multiple effects of a single exposure can be assessed

• Direct measurement of incidence of disease

Retrospective (Cohort Study Design)

existing populations/data, secondary data analysis

• more quickly, cheaper, more efficient for diseases with long incubation/latency periods

• quality of data, lack of adequate details, lack of data of potential confounding, incomplete information for study subjects

Prospective (Cohort study design)

new recruitment, primary data collection

• better data quality, more information, better control for confounding

• cost and loss to follow up

Advantages of cohort studies

• can calculate incidence (risk of developing the disease)

• exposure factor is well defined

• good to study rare exposures

• clear temporal relationship between exposure and outcome

• can collect good information on exposures

disadvantages to cohort studies

• expensive and time consuming

• may need to follow-up participants for along period time

• loss to follow-up may be a problem (prospective studies)

• NOT GOOD for rare outcomes

Case-control studies

• selects the study population based on the disease status

• compare the odds of past exposure to a suspected risk factor between cases and controls

when to use a case-control design

• useful as a first step when searching for a cause of an adverse health outcome (usually cheaper than a cohort study)

  • Next step is often a cohort study

• for a given disease, a case-control study can investigate multiple exposures

• valuable when the disease being investigated is rare

randomized controlled trials

intervention studies are experimental studies in which subjects free of the disease are:

• randomly assigned to the exposure

• followed over for a period of time,

• compared with respect to disease incidence to assess the association between risk factors (exposure) and disease