Overview

One of the strengths of the Pregnancy Risk Assessment Monitoring System (PRAMS) is that each participating state uses a standardized data collection methodology. This standardized approach allows for comparisons among states and for optimal use of the data for single-state or multistate analysis. The complete PRAMS methodology has been described elsewhere.^1,2 The standardized data collection methodology is described in the Centers for Disease Control and Prevention (CDC) PRAMS Model Surveillance Protocol.³ Each state not only follows this basic methodology, but can also customize some procedures to its particular needs. For example, the basic methodology recommends three mailings of the questionnaire packet; however, only two mailings are required.

PRAMS is a mixed-mode surveillance system that combines two modes of data collection. A self-administered mail survey is the primary data collection method. Up to three surveys are mailed to sampled women, and women who do not respond to the mail survey are followed up by telephone. The principles and practices of mail/telephone survey methodology used by CDC are based primarily on the research of Don Dillman.^4,5 A key aspect of his approach is to make numerous and varied contacts with sampled mothers. Below is the sequence of contacts for PRAMS surveillance:

1. Preletter. This letter introduces PRAMS to the sampled mother and informs her that a questionnaire will soon arrive.
   
   
2. Initial Mail Questionnaire Packet. This packet is sent to all sampled mothers 3–7 days after the preletter. Its contents are described below.
   
   
3. Tickler. The tickler serves as a thank you/reminder note. It is sent 7–10 days after the initial mail packet.
   
   
4. Second Mail Questionnaire Packet. This packet is sent 7–14 days after the tickler to all sampled mothers who did not respond.
   
   
5. Third Mail Questionnaire Packet (Optional). This third packet is sent to all remaining nonrespondents 7–14 days after the second questionnaire.
   
   
6. Telephone Follow-Up. Telephone follow-up is initiated for all nonrespondents 7–14 days after the mailing of the last questionnaire.

The series of mailings commences 2–6 months after the mother delivers her infant. Most mothers respond 3–5 months after giving birth. The questionnaire contains items asking about the early postpartum period; thus, the mailings are timed to ensure that all women can respond for this period. The data collection cycle, from the mailing of the preletter to the close of telephone follow-up, lasts approximately 65–85 days.

The mail questionnaire packet contains several items.

• A multipurpose cover letter describes PRAMS, explains how and why the mother was chosen, elicits the mother's cooperation, describes procedures for filling out and returning the questionnaire, explains any incentive or reward, and provides a telephone number to call for additional information. This letter is modified slightly for the second and third mailings, primarily by adding an additional appeal for response.
  
  
• Each state's questionnaire booklet is 14 pages long, has a colorful cover designed by the state, is slightly smaller than an 8 1/2" x 11" sheet of paper, and contains an extra page for comments from the mother. A pre-addressed return envelope with postage is provided.
  
  
• A question-and-answer brochure contains additional information and answers the most frequently asked questions about PRAMS. It can be an important tool to convince the mother to participate.
  
  
• A calendar serves as a memory aid for answering the questions.
  
  
• Some type of participation incentive (sent to all sampled mothers) or reward (sent to all respondents) is included in the packet or explained in the cover letter. Examples of incentives or rewards include coupons for certified birth certificates, participation in a raffle for a cash award, pre-paid telephone cards, bibs, cash (a dollar bill), and magnetic picture frames.

Telephone follow-up begins after the last questionnaire is mailed. States use various sources of telephone numbers to obtain valid numbers. Calls to a particular number are staggered over the time of day and day of the week. The calling period for a batch runs from 2 to 3 weeks. Up to 15 attempts are made to contact a mother. Often, telephone interviewers arrange call-back interviews to accommodate the mother's schedule.

Each month, a stratified sample is drawn from the current birth certificate file. For each of these monthly samples, or "batches,"; the sequence of mail and telephone contacts is attempted. CDC developed and installed a customized tracking system, PRAMTrac, in each state to assist with scheduling mailings and telephone calls, preparing letters, and tracking responses.

In 2002, two states (Montana and North Dakota) conducted point-in-time PRAMS surveys for births during only a portion of the calendar year. North Dakota sampled births that occurred during January through April 2002, and Montana sampled births that occurred during February through May 2002. Except for the truncated time period, sampling and follow-up were done according to the standard PRAMS protocol. The data for these two states were weighted to represent the total number of live births that occurred in 2002. 

Questionnaire and Phases

With the help of numerous persons within and outside CDC, the original PRAMS questionnaire (Phase 1) was developed in 1987. An extensive list of topics was identified and researched for the questionnaire. From this list, questions were developed and tested and ultimately placed on the questionnaire. Participating states used the Phase 1 questionnaire from fall 1988 through 1989. After an evaluation of the Phase 1 questionnaire, CDC and the participating PRAMS states developed the Phase 2 questionnaire and put it in the field during 1990. Although the questionnaire maintained its original structure, some questions were revised, others were deleted, and new questions were added. In 1994, CDC again collaborated with the participating PRAMS states to develop the Phase 3 questionnaire. The revision of the Phase 2 questionnaire was more extensive than the revision in 1989 of the Phase 1 questionnaire. As with the development of the first and second questionnaires, a list of potential topics was extensively researched. Based on this research, questions from the Phase 2 questionnaire were revised or dropped, and new questions were added. The Phase 3 questionnaire retained the original structure as the previous two questionnaires. In fall 1995 and early 1996, states began to use the Phase 3 questionnaire. States implemented use of the Phase 4 questionnaire with January 2000 births.

The PRAMS questionnaire consists of two parts: a core portion that is the same for all states and a state-specific portion tailored to each state's needs. Topics addressed in the PRAMS core questionnaire include unintended (mistimed and unwanted) pregnancy, barriers to and content of prenatal care, infant sleeping position, obstetric history, hospitalizations for pregnancy-related complications, maternal use of alcohol and cigarettes, multivitamin use, economic status, maternal stress, and infant follow-up and well-baby care. The 32 indicators used in this report are found in the core portion of the Phase 4 questionnaire. For the state-specific portion of the questionnaire, states have two options: develop and test their own questions, or select from a series of 124 "standard"; questions on 32 topics that CDC has already developed and tested. These questions reflect additional topics of interest to states. They were originally developed during the revision process for Phase 3, and additional questions have been added since that time.

In addition to the questionnaire created for the mail packet, a telephone version of the core and state-specific questions was also developed for telephone interviews. The interviewer-administered questionnaire is formatted differently than the self-administered questionnaire. It includes prompts and instructions for the interviewer that are not read aloud to the respondent. The interviewer-administered questionnaire format ensures that all interviewers deliver questions and instructions in a uniform manner that is consistent with the mail questionnaire. States with a sizable Hispanic population use a Spanish-language questionnaire for mail and telephone contacts.

Use of Data from Phases 2, 3, and 4

As described earlier in this section, the PRAMS questionnaire has been revised periodically since the original version was completed in 1987. The 2002 PRAMS Surveillance Report contains data collected using questions common to the Phase 2, Phase 3, and Phase 4 versions of the questionnaire.

During the Phase 3 revision of the PRAMS questionnaire, several questions from the Phase 2 questionnaire were modified. While most of the modifications to the Phase 2 questionnaire were minor, for a few questions the changes from Phase 2 to Phase 3 were substantial. In addition, some questions were added to the Phase 3 questionnaire that were not in the Phase 2 instrument. Likewise, during the Phase 4 revision of the PRAMS questionnaire, several questions from the Phase 3 questionnaire were modified. In some cases, the wording of the question was changed slightly. Additionally, several new questions were developed and added to the Phase 4 questionnaire.

Data for 1993–1995 were collected using the Phase 2 questionnaire, except for a small portion of 1995 data for Maine, South Carolina, and West Virginia, which were collected using the Phase 3 questionnaire. (See Appendix A of the PRAMS 1995 Surveillance Report for additional details.)⁶ The Phase 3 questionnaire was implemented by states between July 1995 and July 1996. In some states, data for 1996 include data collected using the Phase 2 and Phase 3 questionnaires. (See Appendix A of the PRAMS 1996 Surveillance Report for additional details.)⁷ All data for 1997–1999 were collected using the Phase 3 questionnaire. The Phase 4 questionnaire was implemented by states for January 2000 births. All data for 2001 and 2002 were collected using the Phase 4 questionnaire. The Phase 4 questionnaire is presented in Appendix D of this report.

Weighting Process

Each participating state draws a stratified, systematic sample of 100–250 new mothers every month from a frame of eligible birth certificates. Most states oversample low-weight births, and many states stratify by the mother's race or ethnicity. Annual sample sizes range from 1,500 to 3,200, divided among 2–6 strata. Typically, the annual sample is large enough for estimating statewide risk-factor proportions within 3.5% (95% confidence interval). Estimated proportions within strata are slightly less precise; typically, they are estimated within 5% (95% confidence interval). (See Appendix B for stratification variables, state annual sample sizes, overall response rates, and weighted response rates.)

Mothers' responses are linked to extracted birth certificate data for analysis. Thus, the PRAMS data set also contains a wealth of demographic and medical information collected through the state's vital records system. The availability of this information for all births is the basis for drawing stratified samples and, ultimately, for generalizing results to the state's entire population of births. The availability of birth certificate data for all sampled women, whether they respond or not, is key to deriving nonresponse weights.

For each respondent, the initial sampling weight is the reciprocal of the sampling fraction applied to the stratum. Sampling fractions in PRAMS range from 1 in 1 (for very low-birthweight strata in small states) to about 1 in 300 (for normal birthweight, nonminority strata in populous states). Corresponding sampling weights, then, range from 1 to 300.

Nonresponse adjustment factors attempt to compensate for the tendency of women having certain characteristics (such as being unmarried or of lower education) to respond at lower rates than do women without these characteristics. Where multivariate analysis shows that these characteristics affected the propensity to respond in a particular stratum, the adjustment factor is the ratio of the sample size in that category to the number of respondents in the category. If analysis shows that no characteristic distinguishes respondents from nonrespondents, the adjustment factor is the ratio of the sample size in that stratum to the number of respondents in the stratum. In the first case, each category so identified has an adjustment factor; in the second, there is a single factor for the whole stratum.

The rationale for applying nonresponse weights is the assumption that nonrespondents would have provided similar answers, on average, to respondents' answers for that stratum and adjustment category. To ensure that cells with few respondents are not distorted by a few women's answers, small categories are collapsed until each cell contains at least 25 respondents. The magnitude of the adjustment for nonresponse depends on the response rate for a category. If 80% (4/5) of the women in a category respond, the nonresponse weight is 1.25 (5/4). Categories with lower response rates have higher nonresponse weights.

The frame noncoverage weights are derived by comparing frame files for a year of births with the calendar year birth tape that states provided to CDC. Omitted records are usually due to late processing and are evenly scattered across the state, but sometimes they are clustered by particular hospitals or counties or even by time of the year. The effect of the noncoverage weights is to bring totals estimated from sample data in line with known totals from the birth tape. In mail/telephone surveillance, the magnitude of noncoverage is small (typically from 1% to 5%), so the adjustment factor for noncoverage is not much greater than 1. To derive these weights, we carried out such a frame omission study to look for problems that occurred during frame construction for all states.

Multiplying together the sampling, nonresponse, and noncoverage components of the weight yields the analysis weight. The analysis weight can be interpreted as the number of women in the population who have characteristics similar to those of the respondent. All weighted results in this report are produced with SUDAAN.⁸ We use SUDAAN for analyzing PRAMS data because it accounts for the complex sampling designs that states employ. It uses first-order Taylor series approximations to calculate appropriate standard errors for the estimates it produces.

Use of Overall and Weighted Response Rates

Surveillance reports for 1995–1997 presented data for states that had fully implemented PRAMS data collection procedures and achieved overall response rates of approximately 70% or higher. The overall response rate represents the total number of mothers completing the survey out of the total number of mothers sampled. Beginning in 1998, the states included in the surveillance reports had fully implemented PRAMS data collection procedures for the year and achieved weighted response rates of 70% or higher. The weighted response rate indicates the proportion of women sampled who completed a survey, adjusted for sample design. The weighted response rate is calculated by (1) multiplying the stratum-specific response rate by the proportion of the population of births that the stratum comprises and (2) adding the stratum-specific response rates across all strata. This weighted rate gives a rough measure of the possible extent of nonresponse bias in statewide estimates. It quantifies how representative the responding women are of the general population and adjusts for the state's oversampling of minority populations. The weighted rate is a counterpart of the design effect, which is a measure of the relative efficiency of a stratified sample, and can be thought of as a non-sampling component of total survey error.

References

1. Gilbert BC, Shulman HB, Fischer LA, Rogers MM. The Pregnancy Risk Assessment Monitoring System (PRAMS): methods and 1996 response rates from 11 states. Maternal and Child Health Journal 1999;3(4):199–209.
   
   
2. Adams MM, Shulman HB, Bruce C, Hogue C, Brogan D, The PRAMS Working Group. The Pregnancy Risk Assessment Monitoring System: design, questionnaire, data collection and response rates. Paediatric and Perinatal Epidemiology 1991;5(3):333–346.
   
   
3. Centers for Disease Control and Prevention (CDC). PRAMS Model Surveillance Protocol, 1999 (Unpublished). 1999.
   
   
4. Dillman DA. Mail and Telephone Surveys: The Total Design Method. New York: John Wiley & Sons; 1978.
   
   
5. Salant PA, Dillman DA. How to Conduct Your Own Survey: Leading Professionals Give You Proven Techniques for Getting Reliable Results. New York: John Wiley & Sons; 1994.
   
   
6. Centers for Disease Control and Prevention (CDC). PRAMS 1995 Surveillance Report. Atlanta, GA: CDC, National Center for Chronic Disease Prevention and Health Promotion, Division of Reproductive Health; 1998.
   
   
7. Centers for Disease Control and Prevention (CDC). PRAMS 1996 Surveillance Report. Atlanta, GA: CDC, National Center for Chronic Disease Prevention and Health Promotion, Division of Reproductive Health; 1999.
   
   
8. Research Triangle Institute (RTI). SUDAAN Language Manual, Release 9.0. Research Triangle Park, NC: RTI; 2004.