Behavioral Risk Factor Surveillance System -- Michigan, 1987-1991

A national health objective for the year 2000 is to implement periodic analysis and publication of each state's progress toward the objectives for each racial/ethnic group that constitutes at least 10% of the state's population (objective 22.5a) (1). In Michigan (1990 population: 9.3 million), blacks represent approximately 12% of the adult population *; prevalence estimates for risk factors for the black population derived from the Behavioral Risk Factor Surveillance System (BRFSS) have varied in consistency because of the limitations of small sample sizes. To improve the precision of risk factor prevalence estimates for blacks in Michigan and to improve measurement of the state's progress toward the national year 2000 objectives for blacks, in 1993, the Michigan Department of Public Health (MDPH) aggregated annual state BRFSS data for 1989-1991. This report summarizes the findings of this analysis and compares them with an analysis of annual state BRFSS data for 1987-1991.

In the Michigan BRFSS, adults aged greater than or equal to 18 years participated in monthly random-digit-dialed telephone interviews. Respondents were asked about behavioral risk factors including smoking, overweight, alcohol use, sedentary lifestyle, high blood pressure, elevated serum cholesterol, and safety-belt nonuse. Annual sample sizes of blacks ranged from approximately 130 to 290 compared with 1175-2150 for whites. The Software for Survey Data Analysis (SUDAAN) was used to calculate prevalence estimates and 95% confidence intervals (2). For the aggregated analysis, BRFSS data for 1989-1991 were combined. The aggregated data were reweighted by the inverse of the relative probability of selection and a poststratification weighting factor using 1990 population figures. This procedure resulted in working sample sizes of 841 blacks and 6134 whites.

During 1987-1991, the annual estimated prevalence rates for two selected risk factors -- smoking and overweight -- varied substantially by year among blacks, ranging from 19.9% to 34.8% and from 24.4% to 39.3%, respectively; there were no consistent increases or decreases in prevalences for either risk factor (Table_1). In comparison, analysis of the aggregated data for 1989-1991 indicated that among blacks the prevalence of smoking was 31.7% and for overweight, 35.2% (Table_2); for both estimates, the confidence intervals were substantially narrower than those for annual estimates. Significant race-specific differences were observed for overweight and seven other risk factors examined (Table_2). Prevalence estimates for the three alcohol-related risk factors (i.e., heavy drinking, binge drinking, and drinking and driving) were significantly higher among whites than among blacks (p less than 0.05, z-test). Prevalence estimates for safety-belt nonuse, sedentary lifestyle, high blood pressure, and never having had serum cholesterol level measured were significantly higher among blacks than among whites (p less than 0.05, z-test). Race-specific differences in prevalence estimates were consistent for both men and women for safety-belt nonuse and for binge drinking. Reported by: AP Rafferty, PhD, HB McGee, MPH, RM Davis, MD, G Van Amburg, MPH, KR Wilcox, MD, State Epidemiologist, Michigan Dept of Public Health. Behavioral Risk Factor Surveillance Br, Office of Surveillance and Analysis, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: The reduction of excess deaths in at-risk minority populations is one of the four primary goals of MDPH. Because of substantial excess mortality from cardiovascular diseases among blacks in Michigan (3), BRFSS data are used to monitor trends in the prevalence of risk factors for this problem (4-8).

The findings in this report indicate that, because of small sample sizes and consequent wide confidence intervals, annual BRFSS prevalence estimates for some population subgroups can obscure trends and statistically significant associations, as well as complicate comparison of such data with that for other subgroups. In contrast, aggregated data may provide more precise estimates and reveal significant associations that can assist in improving the measurement of progress toward national and state health objectives. For example, the aggregated analysis in this report indicates that, because of the higher prevalences of risk factors for cardiovascular diseases (i.e., increased for high blood pressure, overweight, and sedentary lifestyle but lower for having had serum cholesterol level measured) among blacks than among whites, blacks in Michigan should be targeted for health-education programs about cardiovascular disease.

The analysis by MDPH also compared race-specific prevalences of risk factors among blacks and whites. However, race is most likely a risk marker, rather than a risk factor, for high-risk behaviors. Risk markers may be useful for identifying groups at greatest risk for specific high-risk behaviors and for targeting prevention and education efforts. Moreover, race-specific variation in high-risk behavior rates may reflect differences in factors such as socioeconomic status and access to medical care.

The findings in this report are subject to at least two limitations. First, in these analyses, prevalence estimates were not adjusted for differences in socioeconomic status. In Michigan, behavioral risk factor data consistently indicate higher prevalence estimates among persons with less education and lower incomes, which may account for these race-specific differences. Second, in these analyses, cultural factors (e.g., cross-racial survey interviewers and use of jargon) that may account, in part, for observed race-specific differences were not addressed.

The findings of the MDPH study underscore the importance of using different methods of analysis to adjust for the marked annual variations (caused by small sample sizes) in risk factor prevalence estimates for population subgroups. As a result of these findings, MDPH is planning to supplement their annual compilations of BRFSS data with aggregated compilations. The findings in this report suggest that state health departments should periodically compare annual and aggregated BRFSS data to increase the precision of risk factor prevalence estimates for population subgroups and to improve measurement of progress toward national and state health objectives.

References

1. Public Health Service. Healthy people 2000: national health promotion and disease prevention objectives -- full report, with commentary. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50212.

2. Shah BV. Software for Survey Data Analysis (SUDAAN) version 5.5 {Software documentation}. Research Triangle Park, North Carolina: Research Triangle Institute, 1991.

3. Michigan Department of Public Health. Michigan health statistics. Lansing, Michigan: Michigan Department of Public Health, Center for Health Statistics, Office of the State Registrar, 1989.

4. Mayer J, Thrush J, Chan V, Mills EM. Health risk behaviors, 1987. Lansing, Michigan: Michigan Department of Public Health, 1988.

5. Brown SM, Chan V, Mills EM, Ross L, Theisen V. Health risk behaviors, 1988. Lansing, Michigan: Michigan Department of Public Health, 1990.

6. Rafferty AP, ed. Health risk behaviors, 1989. Lansing, Michigan: Michigan Department of Public Health, 1991.

7. Rafferty AP, ed. Health risk behaviors, 1990. Lansing, Michigan: Michigan Department of Public Health, 1992.

8. Rafferty AP, ed. Health risk behaviors, 1991. Lansing, Michigan: Michigan Department of Public Health, 1993.

* In Michigan, blacks and whites are the only racial/ethnic groups that each constitute at least 10% of the population.
Table_1
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TABLE 1. Annual estimated prevalences of smoking * and overweight + among blacks
-- Michigan, Behavioral Risk Factor Surveillance System, 1987-1991 &
=========================================================================================
                       Smoking                  Overweight
                 --------------------       ------------------
    Year          %        (95% CI @)        %        (95% CI)
---------------------------------------------------------------------------------------
    1987         34.8       (+/-7.0)         24.4       (+/-6.3)
    1988         19.9       (+/-6.8)         32.5       (+/-8.0)
    1989         34.5       (+/-6.7)         39.3       (+/-6.8)
    1990         29.4       (+/-6.1)         29.5       (+/-5.7)
    1991         31.5       (+/-6.1)         36.5       (+/-6.9)
---------------------------------------------------------------------------------------
* Defined as current cigarette smoking by a person who has ever smoked 100 cigarettes.
+ Defined as body mass index >=85%.
& Annual sample sizes ranged from 130 to 290 persons aged >=18 years.
@ Confidence interval.
=========================================================================================

TABLE 2. Aggregated analysis * of estimated prevalences of selected behavioral risk factors, by sex and race + -- Michigan,
Behavioral Risk Factor Surveillance System, 1989-1991 &
==============================================================================================================================================================
                                            Men                                        Women                                       Total
                           --------------------------------------      --------------------------------------      -----------------------------------------
                                Blacks               Whites                 Blacks                Whites                Blacks                  Whites
                           -----------------    -----------------      ----------------      ----------------      ----------------      -------------------
Risk factor                 %     (95% CI @)      %      (95% CI)       %      (95% CI)       %      (95% CI)       %      (95% CI)       %      (95% CI)
------------------------------------------------------------------------------------------------------------------------------------------------------------
Safety-belt nonuse **      32.6    (+/-5.9)      25.4    (+/-1.8) ++   28.8    (+/-4.3)      12.4    (+/-1.2) ++   30.5    (+/-3.5)      18.6    (+/-1.1) ++
Heavy drinking &&           4.2    (+/-2.5)       9.5    (+/-1.3) ++    1.4    (+/-1.0)       1.3    (+/-0.4)       2.7    (+/-1.3)       5.2    (+/-0.7) ++
Binge drinking @@          17.0    (+/-4.6)      29.5    (+/-2.0) ++    6.0    (+/-2.3)      10.1    (+/-1.1) ++   10.9    (+/-2.4)      19.4    (+/-1.2) ++
Drinking and driving ***    3.5    (+/-2.2)       6.6    (+/-1.1) ++    1.8    (+/-1.3)       2.0    (+/-0.6)       2.6    (+/-1.2)       4.2    (+/-0.6) ++
Sedentary lifestyle +++    56.3    (+/-6.3)      54.6    (+/-2.1)      66.6    (+/-4.7)      56.8    (+/-1.8) ++   62.0    (+/-3.8)      55.7    (+/-1.4) ++
Overweight &&&             26.7    (+/-5.6)      27.5    (+/-1.9)      42.7    (+/-5.1)      25.3    (+/-1.6) ++   35.2    (+/-3.8)      26.4    (+/-1.3) ++
Smoking @@@                33.7    (+/-6.1)      30.2    (+/-1.9)      30.0    (+/-4.4)      25.8    (+/-1.6)      31.7    (+/-3.6)      27.9    (+/-1.2)
High blood
  pressure ****            26.3    (+/-5.4)      22.1    (+/-1.8)      30.0    (+/-4.3)      24.0    (+/-1.5) ++   28.3    (+/-3.3)      23.1    (+/-1.2) ++
Serum cholesterol level
  never measured           38.6    (+/-6.3)      36.6    (+/-2.1)      37.5    (+/-4.7)      30.2    (+/-1.7) ++   38.0    (+/-3.8)      33.3    (+/-1.3) ++
------------------------------------------------------------------------------------------------------------------------------------------------------------
   * Annual Behavioral Risk Factor Surveillance System data for 1989-1991 were combined; the aggregated data were reweighted by
     the inverse of the relative probability of selection and a poststratification weighting factor using 1990 population figures.
   + Data are presented for blacks and whites only because, in Michigan, these are the only racial/ethnic groups that each constitute
     at least 10% of the population.
   & Annual sample sizes ranged from 1332 to 2412 persons aged >=18 years.
   @ Confidence interval.
  ** Defined as sometimes, seldom, or never wearing safety belts.
  ++ Comparison of prevalence for blacks and whites was statistically significant; p<0.05, z-test.
  && Defined as consuming 60 or more alcoholic beverages per month.
  @@ Defined as at least one episode of consuming five or more alcoholic beverages per occasion during the 30 days preceding the
     interview.
 *** Defined as at least one episode of driving after perhaps consuming too much alcohol during the 30 days preceding the interview.
 +++ Fewer than three 20-minute sessions of leisure-time physical activity per week.
 &&& Body mass index >=85%.
 @@@ Defined as current cigarette smoking by a person who has ever smoked 100 cigarettes.
**** Defined as ever having been told by a health professional that they have high blood pressure.
==============================================================================================================================================================

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