Subgroup analysis requirements

The calculations referred to above are concerned with calculating the sample size required for precision in the analysis of the answers to one particular question. The calculation has to be repeated for every question in the questionnaire. In practice, this turns out to be a largely unmanageable amount of calculation and is rarely undertaken. The size of a sample needed to meet the requirements of every question on the questionnaire is determined by the smallest proportion of respondents likely to answer any particular question on it.

For example, information may be required from both users and non-users of a product. The questionnaire will be devised to ask all respondents the 'filter' question, 'Do you drive a company car?' In 2001 it was known that approximately 6 per cent of households had access to a company car. In a random sample, therefore, 6 per cent of the sample were expected to answer 'yes' and go on to give further information about how they made the decision to take advantage of the company car scheme, whether they owned a private vehicle in addition and so on. In a sample of 500 respondents only 30 were expected to give the data we require about company cars. To expand this number to a more statistically viable level the survey started with a sample of 1800 respondents, anticipating a subsample of 108 households with a company car. If it wanted to identify company car owners who drove five-door hatchbacks, which accounted for 50 per cent of the market, it would have been necessary to start with an overall sample size of 3600 respondents in order to end up with 108 respondents in this category._

It is considerations such as these that determine the overall size of a sample, by working upwards from the analysis requirements of particular sub-groups within a sample. As discussed in Section 7.4.1, weighting can also be used in determining sample size when subgroup analysis is required.

Online Survey Champion

Online Survey Champion

There are people all over the world trying to find ways to make money online. From stay at home moms looking to make a few extra dollars to college students and entrepreneurs, the allure of making your own hours and working from home or from the local coffee shop is very appealing.

Get My Free Ebook


Post a comment