1 BIOS 164 Developing a Sample Design

2 Presentation #8 Lecture Notes:12

3 Some General Rules (1) Talk in language the client can understand. (2) Be honest with the client. (3) Consider all sources of survey error.

4 Some General Rules (4) Find a scientifically sound yet practical solution to design issues. (5) Sketch a plan of action for things to be done next (6) Other: be congenial, adaptable, prompt, compassionate.

5 Design Decision Process: Two General (Interrelated) Steps: (1) Gather information (2) Make decisions

6 Gather Information: What’s Involved? u Analysis objectives: –What are they? –What are the associated parameters? –What are the key measures of interest? –What are their main determinants? –What are the precision requirements for major estimates? u Survey inference: –What population do we wish to study? –What will be the units of observation in that population?

7 Gather Information: What’s Involved? u Population subgroups: –Are any of particular importance for analysis? –Percentage-wise, how large are those sub-groups? u Resources: –How much money and manpower do we have to do the study? –What kinds of expertise do these groups possess?

8 Gather Information: What’s Involved? u Time frame: –What are the beginning and ending dates for the study? –When is data collection scheduled to start –How long can it be allowed to continue? u Sampling frame(s): –What list(s) might be used to pick a sample from this population? –For each list: t What are its units? t How good is its coverage? t What is its content and format? t How accessible is it?

9 Make Decisions: What’s Involved? (1) Survey the best choice? (2) Mode of data collection? (3) Design structure (i.e., number of stages, sampling units in each stage)? (4) Stratification (e.g., stratification variable(s); number and definitions of strata)?

10 Make Decisions: What’s Involved? (5) Selection methods (e.g., SRS, systematic, PPS)? (6) Sample sizes (e.g., respondents, sources of attrition, number selected, allocation to strata and/or stages)? (7) Special design features (e.g., oversampling, measurement of nonsampling errors)? (8) Provisions for analysis (e.g., computation and use of weights; analysis software that properly accounts for the design)?

11 Design Decision Sequence: Bios 164 Student Sampling Projects (1) Explicitly define the population from which the sample will be drawn, including over the time dimension if it applies. (2) What will be the observation units (i.e., the units from which measurements will be taken to obtain population estimates)? (3) What will Y i be (i.e., the measure of interest to be obtained from each observation unit)?

12 Design Decision Sequence: Bios 164 Student Sampling Projects (4) Establish the hierarchy (with observation units as the base) within which a sample could be drawn. *Don’t forget time as a dimension of sampling (with > 1 levels on your hierarchy), if your study is to capture something over time. (5) Decide on how many stages and what sampling units in each stage.

13 Design Decision Sequence: Bios 164 Student Sampling Projects (6) How (if at all) will the sample be stratified? (7) How will the sample be chosen in each stage (e.g., SRS, systematic, PPS)? (8) What will be the sample sizes/allocation among stages and/or strata?

14 Design Summary: Sample Design for Residential Care Study A study designed to better understand the quality of care received by senior citizens living in residential care homes was conducted by in-person interviews in eight subjectively chosen locations, one urban and one rural, in each of the following states: Florida, Maryland, New Jersey, and North Carolina. Each “location” consist- ed of a group of neighboring counties. For purposes of this study, a “residential care home” was defined as a facility for senior citizens (with at least 5 beds for residents) in which residents’ basic living needs are looked after, not their health care needs (as in nursing homes). The majority of residential care homes are “assisted living” and “board-and-care” facilities.

15 The sample of residents for this study was chosen as follows. First, residential care homes within each location were classified as either “small” (5-20 beds) or “large” (>20 beds). Next, using the most current (i.e., at least one year old) list of registered residential care homes in each of the eight locations (obtained from state licens- ing agencies), a separate simple random (without replacement) sample of homes was chosen for each size category in each location. All totaled, 250 residential care homes were selected, and 200 (80%) agreed to participate. All residents in each selected “small” residential care home were included in the study sample. In each of the “large” homes a separate simple random (without replacement) sample of exactly 15 residents was chosen from the billing roster of residents in the home. In all homes combined, 2,500 residents were chosen and 2,000 (80%) completed an interview. Design Summary for Residential Care Study (Continued)

16 Residential Care Home Resident (in 8 locations in 4 states) Stage Description of Sampling Unit (What is being sampled?) Stratification (By what? How many strata? Is sample allocation balanced, proportionate,or disproportionate? Type of Selection Method Used to Choose Sampling Units (e.g., SRS, PPSWOR, etc.) Sample Size (How many sampling units were chosen?) Observation Unit = Design Summary Table RCH (Residential Care Home) # = 16 = 2 x 2 x 4 size urban/ruralstate SRS (WOR) 250 ResidentNone Larger --> SRS (WOR) Smaller --> Take All 2,500