1. BMTRY 738: The Study Population

2. Population/Sample
Population: a complete set of people with a specified set of characteristics
Geographic
Demographic
Clinical
Temporal
Sample: subset of a population

3. Population/Sample Target Population Accessible/Source Population
External Validity (Generalizability)
Accessible/Source Population
External Validity
Intended Population
Internal Validity
Actual Subjects

4. Target Population Step 1: Defining Target Population
Better not to have too many inclusion or exclusion criteria
Increases eligible participants
Increases generalizability
Exclusion
High likelihood of being lost to follow-up
Unable to provide good data
High risk of a side effect

5. Accessible/Source Population
Step 2: Defining Accessible/Source Population
Representative of the Target population
Accessible
Patients at a given clinic
Children at a single school
Trade off between feasibility and bias
Aims of the study are important
Descriptive study, must be representative
Incidence
Prevalence
Associations between exposure and disease

6. Accessible/Source Population
Step 2: Defining Accessible/Source Population
Clinical versus community populations
Population-based study
More expensive
Takes longer
Clinical study
Easy to access patients with a disease
Unable to get prevalence or incidence in the community
Do the clinics in the study have patients representative of patients in the general population

7. Intended Population Step 3: Defining Intended Population
Sample of the source population
Convenience sampling
Anyone who meets the eligibility criteria
Quick and cheap
Consecutive sample, ask everyone within a certain time frame
Volunteer bias
Probability sampling
Simple random sample
Stratified random sample (want to ensure you have enough minority participants in your study)
Systematic samples
Cluster sampling

8. Actual Population Step 4: Actual Population
Response Rate: actual (n)/ intended (n)

9. Project Part 1
If you are not using word, don’t just write on the sheet. Use an extra sheet of paper.
Try to write complete sentences, or at least not one word answers.

10. Project Part 1
Define the target population for the BRFSS. Include inclusion and exclusion criteria.
The target population is adult US citizens in 53 states and territories.
Overview

11. Project Part 1
Define the accessible or source population for the BRFSS. Include inclusion and exclusion criteria that pertain to differentiating between the source and target population. Why do you think this source population was chosen? What are its strengths and weaknesses?
Source Population: adults in 53 states/territories who have a landline home telephone and answer unknown numbers since this is a RDD telephone survey.
Why: This population was chosen for feasibility in both time and money to access a large sample population across a large distance with varying interview times.
Strengths
Weaknesses

12. Project Part 1
List groups of people who are systematically excluded from the BRFSS source population?
Non-landline home telephone users; institutionalized individuals: nursing homes, jails, prisons, rehab/long-term care hospitals; university/college students in university housing (dorms, university apartments);

13. Project Part 1
What is a sampling frame? What sampling frame is used for the BRFSS?
A sampling frame is a listing of units (people) from which the sample is drawn.
The sampling frame used for the BRFSS is a list of all active telephone numbers in the US that could possibly be assigned to households.
Other sampling frames?

14. Project Part 1 Define the intended sample for the BRFSS.
The intended sample for the BRFSS is a representative sample of US citizens in terms of geographic distribution based on the US Census.
Those numbers in highly populated areas are called at a higher rate.

15. Project Part 1 Response Rate BRFSS 2007 South Carolina Pennsylvania
Actual People (n)/ Intended (n)

16. Project Part 1 Data Weighting Representative sample
Want your results to reflect the true population not who responded to the questionnaire.
Design – oversample
Conducting – response rate may differ
BRFSS – nonresponse; noncoverage; adjusts variables of age, race, and sex between the sample and the entire population

17. Project Part 1 Population Based Sampling frame
Is the source population a representative sample of the population?

18. Project Part 1 Population Based versus Clinical Generalizable?
Internal or external validity?

19. Project Part 1
If you invite members from the community to participate in a cohort study, is this population-based research?

20. Project Part 1
BRFSS Study Design?