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Oregon PRAMS Report: 1998-99

Suggested Citation | Executive Summary | Introduction | Methodology | Appendices

Suggested Citation

Department of Human Services, Health Services. Oregon PRAMS First Year Report, 1998-99. Portland, Oregon: Office of Family Health, 2000.

Executive Summary

The Pregnancy Risk Assessment Monitoring System (PRAMS) is a new survey of women in Oregon interviewed approximately 3-4 months after giving birth. PRAMS is intended to help policymakers and program managers plan and evaluate programs for pregnant women and infants.

Oregon PRAMS collects data on maternal behaviors and experiences which, according to prior research, can affect the health of the infant. Topics covered in the interview include: unintended pregnancy; Medicaid coverage; prenatal care; participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC); maternal smoking and alcohol use; prenatal human immunodeficiency virus (HIV) prevention and test counseling; breastfeeding; infant sleep position; and birth control.

In its first year (November 1998 to October 1999 *), 1867 women were interviewed by mail or telephone. Every woman whose newborn had a birth certificate was eligible to be selected for the survey if the baby had been born in Oregon and the mother was a resident of Oregon. A random sample of women was selected each month. Overall, 64.0% of the women contacted statewide completed an interview.

Because one health concern is low birth weight, the PRAMS survey oversampled women whose babies had low birth weight (less than 2500 grams [5 pounds and 8 ounces]). Because women of color are more likely to have an infant with health problems, the PRAMS survey oversampled American Indian, Hispanic, African-American and Asian women. This oversampling was done to make sure that there would be enough responses for a meaningful analysis of issues related to race/ethnicity and low birth weight.

This report provides the statewide answers to the Year 1 questions. To ensure that the results are representative of the Oregon population of new mothers, the answers have been weighted to adjust for the disproportion of oversampling and for any bias caused by non-response.

The Appendices include the actual questions that were asked (Appendix A) and some detail about the methods used in the survey (Appendix B).

Researchers who wish to use PRAMS data should contact Dr. Ken Rosenberg, PRAMS Project Director, 971-673-0237; E-mail:


The Pregnancy Risk Assessment Monitoring System (PRAMS) is part of the Office of Family Health's initiative to use data collection and analysis to support program development, program evaluation, and policy-making. PRAMS is an ongoing, population-based survey designed to identify and monitor selected maternal behaviors and experiences. The experiences and behaviors are those that occur before, during, and shortly after pregnancy. Oregon PRAMS began collecting data in November 1998. The women completed a mailed questionnaire or a telephone interview. They are a random sample of Oregon residents who delivered a live-born infant, as identified from an Oregon birth certificate. *

Oregon PRAMS was modeled after the PRAMS program run (since 1987) by the Centers for Disease Control and Prevention (CDC) and selected state health departments. Oregon PRAMS collects data on a variety of topics, including unintended pregnancy, prenatal care, Medicaid coverage, breastfeeding, smoking, drinking, infant sleep position, birth control, prenatal human immunodeficiency virus (HIV) prevention and HIV test counseling, and participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC).

This report presents an overview of the Oregon PRAMS project, a discussion of the Oregon PRAMS methodology, and a summary of the responses to the Oregon PRAMS survey for the first 12 months. The bulk of the report is the tabulation of the answers to the survey questions. Appendix A presents the English-language mailed version of the survey. The Spanish-language mailed version and the phone interview scripts (in English and Spanish) are available upon request to the PRAMS Project Director.

This report does not contain a detailed analysis of each of the topics identified above. Our expectation is that programs and health researchers will analyze PRAMS data. Policymakers will then be able to use these analyses to monitor progress toward pregnancy-related health objectives. We are publishing the first PRAMS report in this form, with no analysis, to inform the broadest possible audience, as early as possible, of exactly what information we have -- so that programs and policymakers will think about how this and future data can inform their missions. We view dissemination of the data included in this report as a key step in the translation of PRAMS data into public health action, a primary goal for PRAMS. We hope that this report will serve as a valuable reference document for use in public health planning and policy development. Our goal is that analyses of these data will affect the work in local and state Maternal and Child Health (MCH) programs and perhaps generate questions for future versions of PRAMS.


Every month, a stratified random sample of 200-300 new mothers was selected from a frame of eligible birth certificates. The sampling frame included all Oregon resident women whose babies had been born in Oregon 60-180 days before the selection date and who had not previously been in the sampling frame. The PRAMS survey oversampled American Indian, Hispanic, African-American and Asian women and women whose babies had a birth weight less than 2500 grams (5 pounds and 8 ounces). This oversampling provided a sufficient number of responses to permit meaningful analysis of health risks related to race/ethnicity and low birth weight. Most women were contacted about 3 months after their baby was born. Each sampled mother was mailed an explanatory letter that introduced the survey, followed by a package containing the 20-page questionnaire one week later. A second package, containing the same questionnaire was mailed about 3 weeks later to those who did not respond. Telephone interviews were conducted by staff from Clearwater Research, Inc. of Boise, Idaho. Clearwater staff then telephoned those mothers who did not respond to the mailed survey and attempted to complete an interview.

Before analysis, the interview responses were weighted to make them representative of Oregon women with live births. Responses were first weighted to account for the sampling design (oversampling by race/ethnicity and birth weight): "over-sampling adjustment." The second layer of weighting ("unit non-response") accounted for non-response (e.g., young women were less likely to respond than older women). The third layer of weighting ("non-coverage adjustment") accounted for the very few birth certificates (about 0.03%) that were never in the sampling frame, most of whom are adopted or whose birth certificates were processed more than 180 days after birth (who were intentionally excluded). Details of the weighting methodology appear in Appendix D.Additional information about the PRAMS methodology can be found in the appendices. Appendix B contains the questions that were asked in first 12 months of Oregon PRAMS. (As was noted above, copies of the later English version, as well as copies of the Spanish mailed questionnaire and the English and Spanish telephone interview scripts, are available upon request.) Appendix C describes the PRAMS data collection methodology in detail. Appendix D contains details on weighting, sample sizes, response rates, and stratification variables.

All tables in the report were produced using weighted PRAMS data. Percentages were calculated using SPSS. The number of respondents reported in each table is the number of women who answered that question. All missing (blank and "don't know") observations are excluded, unless "don't know" is an answer option.

Note that PRAMS data are representative of women whose pregnancies resulted in a live birth and are not generalizable to all pregnant women.


Appendix A: PRAMS 1998-99 Survey in English (pdf)

One strength of the PRAMS surveillance system is the standardized data collection, allowing for observation of Oregon trends over time and comparisons between Oregon and other states.

PRAMS is a mixed-mode surveillance system that combines two modes of data collection. The primary data collection method is a mailed questionnaire. Women who are indicated as being Hispanic on the birth certificate receive the survey and all materials in both English and Spanish. Multiple attempts are made by mail and then by telephone to follow up with non-respondents. Phone surveys are also available in both English and Spanish.

The following is the sequence of contacts for PRAMS surveillance:

  1. Preletter. This letter introduces PRAMS to the mother and informs her that a questionnaire will arrive soon.
  2. Initial mail questionnaire packet. This packet is sent to all sampled mothers about 7 days after the preletter. Its contents are described subsequently. Mothers are instructed to call the Oregon SafeNet toll-free number if they want to be interviewed by phone rather than complete the written survey.
  3. Tickler. The tickler serves as thank you or reminder note. It is sent about 7 days after the initial mail packet.
  4. Second mail questionnaire packet. This packet is sent to all sampled mothers who have not yet responded 14 days after the tickler was sent.
  5. Telephone follow-up. Telephone follow-up is initiated for all non-respondents 14 days afer mailing the second questionnaire. It is done, in both English and Spanish, by Clearwater Research, Inc., Boise, Idaho.
The series of mailings commences two to four months after delivery. 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 mailing the preletter to the close of telephone follow-up lasts approximately 60-70 days. Each month a stratified random sample is drawn from the current birth certificate file. This sequence of contacts is attempted for each of these monthly samples, or "batches." The median time from birth to completion of the survey is four months.

The mail packets contain the following items:

  1. A multipurpose cover letter that 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 the incentive and provides a toll-free telephone number for additional information. This letter is modified slightly in the second mailing, primarily by adding an additional appeal for response.
  2. The questionnaire booklet. The questionnaire booklet is 20 pages long, has a colorful cover, is [7"x8.5"] and contains two blank pages for comments from the mother. A self-addressed return envelope with postage is provided.
  3. An information sheet that contains answers to the questions most frequently asked about PRAMS. It can be an important tool to convince the mother to participate.
  4. A three-year calendar to be used as a memory aid for answering the questions.
  5. Incentive: each woman who returns the first survey within 8 weeks is entered into a drawing; one woman each month wins $200 in gift certificates from Fred Meyer stores.
In addition to the questionnaire created for the mail packet, a telephone version of the questionnaire has also been developed for use during the telephone phase. Telephone follow-up begins six weeks after the lst questionnaire is mailed (see Appendix of timetable derived from ohd1\prams.19n). Various sources of telephone numbers are used to obtain valid phone numbers. Calls to a particular number are staggered over different times of the day and different days of the week. Up to 15 attempts, on each phone number, are made to contact a mother.

The interviewer-administered questionnaire includes the same content as the self-administered version, however some questions have been reformmatted to facilitate reading them aloud to the mother. Alternate interview arrangements have been made for women who speak neither English nor Spanish.

PRAMS Weighting Process

This report includes data from two versions of the PRAMS survey. The first was used from November 1998 to March 1999 and the second was used from April 1999 to October 1999. The only difference between the versions is in Question 74, the categorizations of answers about family income, and reflects changes in the federal poverty level guidelines.

Ascertainment of family income:
A review of the literature about asking people their income led to the creation of a two-question sequence; the first question asks women their family income and the second question asks them to select the income range that includes their family income. Income questions continue to have slightly greater non-response than other questions. Because PRAMS data is being used to evaluate the recent family planning expansion waiver (to prevent unintended pregnancy in women with 100-185% of the federal poverty level) it was particularly important to obtain precise income information. The income categories are changed annually to reflect changes in the federally defined poverty level that go into effect every April. For example, new federal poverty guidelines going into effect in April 1998 reflect income at time of conception for babies born in January 1999; typically PRAMS is surveying those women in April 1999.


Note that the data presented here are weighted data: estimates of how a random sample of Oregon women would answer these questions. The data represent information from women who answered the questions in all six strata, and are weighted for state-wide averages. It will be possible to analyze the answers to PRAMS questions for any subset of sampled women, including by birth weight or race/ethnicity (the oversampled strata).

I. Sampling

The 1997 total births from Oregon resident mothers who gave birth in Oregon was used as the basis for determining sample sizes. This population was broken down into normal birthweight (NBW, birthweight > 2500g) and low birthweight (LBW, birthweight < 2500g); and race/ethnicity categories. The Oregon birth certificate race/ethnicity categories are different from CDC's categories (White, Hispanic, Black, American Indian, and Asian/Pacific Islander) and program codes were created to match Oregon codes to CDC-PRAMS categories.

CDC's proposed initial allocation was 400 for each race/ethnicity category per year. Assignment to normal and low birthweight in each race/ethnicity group was based on the derived population proportions. Oregon PRAMS oversampled White Low Birthweight to match White Normal Birthweight at 400 each. Hence, the total initial allocation for the state was 2,400 per year. The finite population correction factor was used to adjust allocations where the sampling fraction exceeded 1 in 10. Hence, all groups except NBW White and Hispanic were adjusted using the finite correction factor. After this, the resulting group sample size was inflated by dividing by 70%, the intended response rate. The group sample sizes were transformed into the resulting fractions (expressed as decimals) for each race/ethnicity category and ultimately expressed as common, easy to remember fractions. These fractions were multiplied with the actual counts for each of the 10 birthweight and race/ethnicity groups to determine the actual estimated yearly sample size. Dividing the result by 12 gives an estimate for the monthly sample size. The actual procedure was to follow these series of steps for each month.

Sampling Proportions:

  • NBW White: 1/65
  • LBW White: 1/4
  • Hispanic: 1/10
  • African Am: 9/20
  • Am Indian/Alaskan: 1/2
  • Asian/Pacific Islander: 1/4
Most of the mothers sampled in each month had given birth 60 to 90 days prior to the drawing date. However, mothers who were not included in the sampling frame but were eligible in past drawings were given a chance to be picked in succeeding drawings so long as they delivered their babies no more than 180 days ago. These occur primarily when there are late birth certificate entries at Vital Statistics. Multiple births were noted and the mother was given only one chance to be in the sampling frame. If picked, the Oregon PRAMS cover letter asks the mother to answer the questions as they pertain to one specific baby. Live births which resulted in early death for the babies were also noted. A different cover letter was sent, but the same questionnaire was provided.

In the first year (November 1998 to October 1999) we mailed the survey to 2,919 women. This number was bigger than the initial projections and may be primarily due to the increase in the number of total births and the policy of rounding up to the next higher integer in each of the 10 sampling categories. A total of 1,867 (64.0%)responses were received either in the first or second mailing, or in the telephone interviews.

II. Weighting

Weighting is done in three steps. Weight I represents the over-sampling and strata adjustment, Weight II the unit non-response adjustment, and Weight III the non-coverage adjustment. The final weight is the product of these three weights. The final report represents the weighted percentages of the different responses to each question.

A. Weight I: Over-sampling and strata adjustment

The stratification weight is the total number of eligible mothers for the year divided by the actual number sampled.

B. Weight II: Unit Non-response

CDC identified the variables marital status, high education, low education, parity, high age, low age, and 1st trimester prenatal care as possible indicators of a mother's inclination to respond. Each one of these variables were defined in the following manner:

MARSTAT 0 All Else Marital Status
1 Married
HIGHEDUC 0 At most K12 High Education
1 College +
LOWEDUC 0 At least K12 Low Education
1 < K12
PARITY 0 First born Parity
1 Not first born
AGEHIGH 0 All Else High Age
1 30 <= Age < = 49
AGELOW 0 All Else Low Age
1 11 <= Age < = 19
PNCHIGH 0 Late/No PNC Prenatal care in 1st trimester
1 1st Trimester PNC
Another newly defined variable is:
RESPONSE 0 Non-Response
1 Response
The entire sample for the year is used for the binary logistic regression as the first step of Classification and Regression Tree (CART) analysis. The dependent variable is RESPONSE and the independent variables were all the preceding defined variables. The object is to determine groups of mothers with similar demographic characteristics whose response patterns are statistically significantly different from other groups. The CART process is iterative and is continued until there are either no more statistically significantly different partitions based on the 7 variables or when any of the nth partitions or nodes have total responses less than 25. Nodes with similar response patterns are merged and re-checked for any possible partitions.

This procedure is undertaken in each of the 6 strata (NBW White, LBW White, Hispanic, African American, American Indian/Alaskan Native, and Asian and Pacific Islander).

The CART analysis yielded the following partitions:

  1. NBW White
    1. HIGHEDUC = 1
    2. HIGHEDUC = 0 and AGEHIGH = 0
    3. HIGHEDUC = 0 and AGEHIGH = 1
  2. LBW White
    1. MARSTAT = 0
    2. MARSTAT = 1
  3. Hispanic
    1. MARSTAT = 0
    2. MARSTAT = 1
  4. African American
    1. LOWEDUC = 0
    2. LOWEDUC = 1
  5. American Indian/Alaskan Native
    1. PNCHIGH = 0
    2. PNCHIGH = 1 and (MARSTAT = 1 or (MARSTAT = 0 and AGELOW = 1))
    3. PNCHIGH = 1 and MARSTAT = 0 and AGELOW = 0
  6. Asian/Pacific Islander
    1. LOWEDUC = 0
    2. LOWEDUC = 1
The corresponding weights for each one of the partitions is the total partition or node sample size divided by the number of respondents.

C. Weight III: Non-coverage adjustment

Weight III is the ratio of the current birth certificate file list of all eligible births during the first year to the cumulative sampling frame in the same time period. Ineligible births are those siblings of multiple births which were not chosen to be in the sampling frame.


Eligible Mothers: must be an Oregon Resident and the baby must be born in Oregon.
Only 1 of any twins or triplets are given a chance to be sampled. PRAMS Year 1: Dates of birth from August 1, 1998 to August 9, 1999

Total Births for Year 1:
Total Eligible Births for PRAMS inclusion: 45,043

Total Sampled: 2,919
Total Respondents: 1,867

SPSS Syntax code for Weighting:

*PRAMS Weighting Scheme
* d:\finalwt\py1fwt2.sps
* als 08/17/00 N (Birth Certificate) = 45,043 N (PRAMS) = 45,054

* I. Weight 1: Stratum

if (bcrace = "Hispanic") weight1 = 6680/686.
if (bcrace = "AI/AN") weight1 = 660/339.
if (bcrace = "Asian/PI") weight1 = 2080/521.
if (bcrace = "African Am") weight1 = 910/422.
if (bcrace = "White" and wtcat = "NBW") weight1 = 33162/537.
if (bcrace = "White" and wtcat = "LBW") weight1 = 1562/414.

* II. Weight 2: Unit Non-response
numeric weight2 (F5.2).

*1) American Indian/Alaskan Native

if (bcrace = "AI/AN" and pnchigh = 0) weight2 = 103/46.
if (bcrace = "AI/AN" and pnchigh = 1 and (marstat = 1 or (marstat = 0 and agelow = 1))) weight2 =
if (bcrace = "AI/AN" and pnchigh = 1 and marstat = 0 and agelow = 0) weight2 = 80/44.

*2) Hispanic

if (bcrace = "Hispanic" and marstat = 0) weight2 = 285/166.
if (bcrace = "Hispanic" and marstat = 1) weight2 = 401/277.

*3) African American

if (bcrace = "African Am" and loweduc = 0) weight2 = 329/177.
if (bcrace = "African Am" and loweduc = 1) weight2 = 93/34.

*4) Asian/Pacific Islander

if (bcrace = "Asian/PI" and loweduc = 0) weight2 = 445/275.
if (bcrace = "Asian/PI" and loweduc = 1) weight2 = 76/31.

*5) NBW White

if (bcrace = "White" and wtcat = "NBW" and higheduc = 1) weight2 = 267/224.
if (bcrace = "White" and wtcat = "NBW" and higheduc = 0 and agehigh = 0) weight2 = 218/162.
if (bcrace = "White" and wtcat = "NBW" and higheduc = 0 and agehigh = 1) weight2 = 52/29.

*6) LBW White

if (bcrace = "White" and wtcat = "LBW" and marstat = 0) weight2 = 151/91.
if (bcrace = "White" and wtcat = "LBW" and marstat = 1) weight2 = 263/187.

*III. Weight3: Coverage

numeric weight3 (F5.2).
compute weight3 = 45043/45054.

*IV. Final Weight

numeric fweight (F6.2).
compute fweight = weight1*weight2*weight3.