[This is another note on using the SDA interface to analyze IPUMS that is intended for students in my Introduction to Social Demography. I am posting it here rather than my class website because it may be of interest to others who are using the IPUMS for teaching.]
The ACS includes some very useful questions on demographic events within the last year, including births, marriages, and divorces within the last year. Many students have indicated an interest in studying birth rates, so I am writing this note to provide some help on using the ACS data from 2001 to the present to calculate basic rates.
The ACS data on IPUMS includes a variable that indicates whether someone has had a birth in the last year. It is 0 for cases where the information is not available, 1 if no birth occurred, and 2 if a birth occurred. We can use this to approximate fertility rates if we restrict (using the filter) to observations where fertyr was 1 or 2, use comparison of means, and remember to subtract 1 from the means that appear in the table. We need to subtract because 1 indicates no births, while 2 indicates a birth.
To calculate age-specific rates by year from 2001 to 2009, I set up a calculation with the following…
Dependent variable: fertyr
Row: age(r:10-14;15-19;20-24;25-29;30-34;35-39;40-44;45-49)
Column: year
Selection filter: fertyr(1-2) sex(2) age(10-49)
Also, under ‘Change number of decimal places to display’, I selected 3, so that whatever the mean was, subtracting 1 and multiplying by 1000 would yield a rate per thousand.
To address the problem associated with fertyr being 1 for people who haven’t had a birth, and 2 for people who have had a birth, we could recode fertyr so that 0 means no births, and 1 means a birth. In that case, the mean would actually be the proportion of people who have had a birth:
Dependent variable: feryr(0=1;1=2).
Of course, instead of using year as the column variable, one could use race, or some other variable of interest.
Just remember that what is reported in each cell of the output is the mean number of children in the last year plus one, so that when you prepare tables to turn in, you subtract one from each of the values in the cells in the output.