Asking someones age is generally through of  the height of rudeness, yet in surveys the age of your respondents is critical demographic data. Data accuracy around this question is pretty important and recent research shows that the way you ask this question has a strong influence on how it will be answered.

Philip Gendall and Benjamin Healey (my old market research lecturer and backwards market research guru) have done a bit of digging round to see who researchers can best pose this question to respondents without having 80% of your respondents saying they have just turned 21.

In their article ‘Asking the age question in mail and online surveys’ (2008) they look at the age question and investiagte how it can minimise item non-response and maximise accuracy. They found that the best way to ask the age question in order to maximise accuracy and response rates was to ask the respondent either their date of birth or the year that they were born. As they put it themselves:

“This format appears to work well in all survey modes, is parsimonious of questionnaire space, is easy to administer, and generally produces low non-response and high accuracy.”

They also suggest when using online surveys staying away from drop-down boxes. Data entry errors can easily occur with drop-down boxes with respondents inadvertently changing their response.

One word of caution I would have it to think seriously before asking anyone their date of birth. In most surveys this level of accuracy is not actually required and I think asking the date of birth question is likely to increase your non-responce rates. With identity theft now firmly in the public mind people are thinking twice about giving out personal infromation, espeically infromation as sensitive as someone date of birth. My advice then is to stick with year of birth. You get the data you need and you reduce your non-responce error.