# 1999 Adult Asthma Data: Technical Information

## Viewing and Printing Tables and Maps

Maps are not provided for 1999 data because of the limited number of states that asked the asthma questions.

Tables are provided in PDF format and can easily be printed in portrait orientation using Adobe Acrobat.

## BRFSS Questionnaire

Interviews are conducted in each state among noninstitutionalized civilian adults (18 years of age or older) living in households with a telephone (Chapter 1, page xviii of the BRFSS User's Guide).

In 1999 only 17 states and the District of Columbia included the asthma questions. Data are taken from responses to the following questions from the 1999 BRFSS Asthma Optional Module.

**Lifetime asthma:**

Did a doctor ever tell you that you had asthma?

(variable name: asthma)

**Current asthma:**

If the response to the above question was Yes, then the following question was asked: Do you still have asthma?

(variable name: asthnow)

Subgroup tables are based on data from the following questions:

Survey Question | Variable name | Codes used |
---|---|---|

10.18 Indicate sex of respondent | sex | 1 = male 2 = female |

10.01 What is your age? | age | Grouped into: 18-24, 25-34, 35-44, 45-54, 55-64, 65+ |

10.02 What is your race? | orace | 1 = white 2 = black 3,4,5 = other |

Race/ethnicity - a combination of response to 10.02 and 10.03 Are you of Spanish or Hispanic origin? | race | 1 = white, non-Hispanic 2 = black, non-Hispanic 3,4,5 = Hispanic 6,7,8 = Other non-Hispanic |

10.06 What is the highest grade or year of school completed? | educa | 1,2,3 = <HS graduate 4 = HS graduate 5 = some college 6 = college graduate |

10.08 Is your annual household income from all sources: a. Less than $25,000? etc. | income2 | 1,2 = <$15,000 3,4 = $15,000-$24,999 5,6 = $25,000-$49,999 7 = $50,000-$74,999 8 = $75,000+ |

## Survey Design and Sample Weights

The survey design is described in the BRFSS User's Guide [PDF, 1.7 Mb].

Top of Page## Data Analysis

##### Data Used:

The BRFSS 1999 Survey Data file was used to calculate estimates for the 17 states and the District of Columbia.

##### Software:

Prevalence and standard error estimates were calculated using SUDAAN Release 7.5 (Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709).

##### Data Management:

Only respondents with values of the variables as described in the table above are included in each prevalence table. Responses of "don't know/not sure," "refused" or missing values, were excluded.

For the question "Do you still have asthma?" respondents included only those who answered "Yes" to the question "Did a doctor ever tell you that you had asthma?" (**asthma**). Responses to the question, "Do you still have asthma?" (**asthnow**) were subsequently recoded (assigned a value of 2 = No) if the respondent answered "No" to the first question. Otherwise, this variable (**asthnow**) was unchanged.

##### Ratio of Adult Self-Reported Current to Lifetime Asthma by State:

The ratio is a survey-based estimate of prevalence of asthma based on those surveyed who responded "Yes" to question 3.1, "Did a doctor ever tell you that you had asthma?" It is *not* a rate ratio.

##### Table Conventions:

In the tables, states are listed in Federal Information Processing Standard (FIPS) code order.

Top of Page## Small Sample Size

When sample sizes in cells are less than 50, as they are in some of the subgroup tables, the standard error may be large relative to the prevalence value, leading to a wide 95% confidence interval. Caution should be used in interpreting such "imprecise" estimates of prevalence.

Also, when one or more of the following situations occurred, the indicated solutions were applied:

Situation | Solution |
---|---|

1. The normal distribution approximation to the binomial distribution did not apply. | 1. Values for the standard error and the 95% confidence interval were not provided. |

2. If the normal distribution approximation does apply, it is appropriate to use values of the t-distribution to compute confidence intervals. | 2. Two-sided 95% confidence interval values from the t-distribution with (n-1) degrees of freedom (where n is the number of observations for the subgroup) were used. |

3. The lower limit of the 95% confidence interval was negative. | 3. The lower limit was set to zero. |

- Page last reviewed: April 27, 2009
- Page last updated: April 27, 2009
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