Technical Information and Data

Numbered Memos

BRFSS POLICY MEMO 2003.2
Sample Provision Policy

BSB has developed a mechanism by which BRFSS projects can obtain sample records from a commercial sample provider through BSB at no direct cost to them. Projects are encouraged to obtain BRFSS sample through this mechanism. The advantages for the projects and for the BRFSS as a whole are the assurance of uniformly and appropriately generated sample and the inclusion of a large number of fields on the sample records useful for improving data collection as well as methodological and substantive analyses. BSB will continue to provide sample records for all projects which request them. BSB will have the sample records generated quarterly but the sample records will be provided monthly. The provisions of this policy apply to contractors collecting data for projects as well as to projects collecting their own data.

Any sample obtained through BSB is for BRFSS data collection only. In particular, BSB will not provide sample for BRFSS-like studies, even if they are using the BRFSS questionnaire and the data are being collected at the same time as BRFSS.

BSB will routinely review sample usage by projects. If a project is consistently not releasing most of the sample it receives or if there is strong evidence that the project is deviating from BRFSS protocol in such a way that it could significantly increase its sampling efficiency (completion rate) by adhering to BRFSS protocol, BSB may decrease sample provided during a data collection year. In every case, BSB will consult extensively with the project coordinator before decreasing sample.

Because the contract with the sample provider is a federal contract, BSB is required to place the orders for sample. Thus, BSB will serve as intermediary for ordering sample and for resolving issues regarding sample. Projects should contact BSB staff, not the sample vendor, about any questions or issues regarding their sample.

Projects are responsible for reporting any change in their designated sample recipient to BSB prior to the effective dates of change.

Requests for additional sample: Projects may request additional sample during a data collection year either to meet or to increase their target monthly number of completes using the following guidelines:

1. A project not meeting the monthly target(s) may request additional sample if most of its sample is being released and the project is using it in accordance with BRFSS protocol. (Projects with multiple geographic strata will have a target for each stratum. For those projects, each stratum will be treated separately.)
    
2. The total quantity of increases in sample sizes that BSB is able to accommodate during a data collection year is limited. Although BSB plans for adjustments of sample sizes during a data collection year, the general level of funding is based on target sample sizes provided by projects in the Sampling Design Characteristics Form in October preceding the data collection year. Approval of a large increase in target number of completes by a project or several projects during a data collection year could lead to a subsequent inability to provide more sample to a project that is not meeting its original target number of completes. For this reason, BSB must consider requests from projects for additional sample for purposes of increasing target sample size on a case-by-case basis. Projects should initially contact their Project Officers with such requests.

Project Purchase of Sample: Coordinators or contractors who are provided sample by BSB may purchase additional sample for BRFSS at their own expense if prior, written agreement of the Survey Operations Section Chief or the BSB Branch Chief has been obtained. Data from sample purchased without the prior, written agreement of the Survey Operations Team Leader or the BSB Branch Chief will not be processed as part of the BRFSS annual file. Any additional sample purchased by the project must meet the same standards as that purchased by BSB. Projects may not generate additional sample for BRFSS independently.

Implementation of Sample Provision Policy

Requesting Change in Sample Size During a Data Collection Year

A project wishing to obtain additional sample during a quarter should submit an e-mail request to the Sample Coordinator at least three weeks prior to the month in which additional sample is needed (e.g., May 10 for June 1 sample). A project wishing to increase or decrease sample size at the start of a quarter should submit an e-mail request to the Sample Coordinator at least one month prior to start of the new quarter. (e.g. June 1 for third quarter sample). (Prior quarter's sample amount will be e-mailed to a project=s BRFSS coordinator for review one month prior to the start of the new quarter.)

Provide the following information by stratum to support your request:

1. Sample Record Request—
   

   Stratum Number	1
   First Month Sample Needed	July
   Current Sample Amt.	1000
   Additional Amount (in 50's)	200
   New Total Amount	1200




2. Prior Month(s) History by Stratum—

   Stratum	Month	Target Completes	Actual Completes
   1	January	250	236
   	February	250	195
   	March	250	207
   	April	250	186




3. Identify any other factors that may have influenced number of completes.

E-mail call history files to BSB.

1. Ci3 CATI Windows projects should include a zipped file of all files in their study directory for the three most recently completed months in the calendar year.
   
2. Other projects should contact Survey Operations Team Leader to discuss how to send call history files.

Review of Sample Requests

BSB will review requests as they are received and follow through with the BSB sample provider to ensure timely receipt of sample. The review of a request to increase sample size will involve obtaining answers to at least the questions below. Other questions may also be addressed depending on the situation of an individual project. Additional questions may also be addressed as BSB gains more experience with requests for additional sample records and expanded quality control procedures.

1. Has the project routinely released almost all replicates in the strata for which additional sample records are being requested and has the project released all to-be-called numbers in the released strata?
    
2. Has the project substantially followed the BRFSS callback rules, that is, obtained in CATI an appropriate final disposition for almost all numbers, including the calling of unresolved numbers at least 15 times, with at least 3 calls on weekdays, 3 on weeknights, and 3 on weekends, and over at least 5 calling occasions?
    
3. Does the pattern of final disposition codes indicate that the project may be missing significant numbers of households in its sample. For example, does the project have extremely large percentages of unresolved numbers among listed one-plus household numbers and not-listed one-plus block numbers?
    
4. Does the pattern of final disposition codes indicate that the project is experiencing extremely low cooperation or response rates?

The intention of BSB is to approve all requests from projects for which the answers are ‘Yes’ to the first two questions and ‘No’ to the last two questions. Answers of ‘No’ to the first two questions and ‘Yes’ to the last two questions could imply the existence of substantial numbers of additional completes in the current sample and thus the possibility of an extreme amount of bias in the data and the non-comparability of the data to those of other BRFSS projects. In such cases, BSB may ask a project to make appropriate changes in its practices before approving a request for additional sample records.

For states which do not have any of the problems identified above, BSB will estimate the number of sample records needed, by stratum, based on the following formula:

Total number of replicates needed per month = Target monthly number of completes divided by Expected number of completes per replicate, where

Expected number of completes per replicate = [The average number of listed household numbers in previously generated replicates (for up a year previously) times the completion rate among listed household numbers (for up a year previously)] plus [the average number of not-listed one-plus block numbers in previously generated replicates (for up a year previously) times the completion rate among not-listed one-plus block numbers (for up a year previously)].

The resulting Total number of replicates needed per month will be routinely rounded up to the next whole number. If the fractional part of the initial calculation is greater than .75, the Total number of replicates will be rounded up an additional whole number. An additional adjustment may be made in agreement with the project under special circumstances.

For example, suppose a project has two geographic strata. The total number of replicates needed for each stratum has to be calculated separately. Suppose that the replicates of 50 contain an average of 11.2 listed household numbers and that the completion rate among the listed household numbers is .55. Suppose further that the replicates in the stratum contain an average of 10.5 not-listed one-plus-block numbers and that the completion rate among these numbers is .30. The expected number of completes per replicate would be (11.2 x .55) + (10.5 x .30) = 9.31. Next, suppose that the monthly target number of completes in the stratum is 75. Then, the total number of replicates needed per month for that stratum would be 75 / 9.31 = 8.06, which would be rounded up to 9. The number of replicates needed per month for the second stratum would be calculated separately in the same way. If a state has only one geographic stratum, the above procedure is used to calculate the single stratum.

This formula takes into account previous project experiences with sample records and with outcome rates. BSB recommends that projects receiving sample from BSB in the previous year and not experiencing any of the problems indicated above use this formula to calculate their annual sample requests.

For states with extremely low completion rates, a rate higher than the observed rate might be substituted.

Purchase of Additional Sample Records by Projects, Including Contractors, With Their Own Funds

Projects or their contractors wishing to purchase additional sample records from BSB's sample provider may do so if (1) they meet the criteria specified above for requests for additional sample, including agreement of BSB, (2) the sample records contain the same fields in the same format as sample purchased through BSB, and (3) they make arrangements for BSB to receive the additional sample records. BSB will process data records from sample purchased directly by projects only if the Survey Operations Team Leader or the BSB Branch Chief has agreed to do so in writing beforehand and they meet these three criteria.

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This page last reviewed June 22, 2005

United States Department of Health and Human Services
Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
Division of Adult and Community Health