Calculating age from a date of birth

These instructions tell you how to create variables to calculate the respondent's age from their date of birth and then put the respondents into age bands, based on the difference between a date of birth variable and the date function today. The instructions also apply if you have another date question in the questionnaire, which you want to use instead of today.

For this example, the date of birth variable is Q1. It assumes a four-digit year.

1. Click to create a new variable. Specify the Variable Details as:

   Name: Age

   Label: Calculated age in years

   Type: Derived (the variable will derive its data from other existing variables).

   Response: Quantity (the response will be a numeric value for each case).

   

2. Specify the Code Values to calculate the number of years:

Code	Code Label	Value
NA	Not Asked	Q1 Missing
OK	Valid	(today-Q1a)\365.25

Note the use of \ to extract the whole number of years.

1. Click to save the variable. You can then use this to analyse respondents' ages.

   The Not Asked value is specified to ensure that the calculation is only performed if data exists for the date question.

2. To band the respondents into age groups, create a new variable:

   Name: Agegroup

   Label: Age groups

   Type: Derived

   Response: Single (each respondent will only fall into one of the new codes).

   

3. Specify the Code Details:

   Code	Code Label	Value
   1	Up to 18	Age <= 18
   2	19 to 24	Age <= 24
   3	25 to 34	Age <= 34
   4	35 to 44	Age <= 44
   5	45 to 54	Age <= 54
   6	55 to 64	Age <= 64
   7	65 plus	true

   The codes are assigned in order, so all responses that have not been sorted into previous bands appear as 65 plus.

4. Click to save the variable.

See Also Date formats Date Functions Categorising date responses Using a date function to determine the day of the week of a date