Strategy Survival Guide

• The "population" and “sub-groups” to be studied: the sample to be surveyed needs to be carefully
selected to ensure that the findings are similar to those found amongst your target population. There
are three basic types of sampling:
1. Probability sampling. This includes random sampling, systematic sampling (similar to
random sampling but some element of selection e.g. every 100th person in directory), and
cluster sampling (e.g. pupils in a particular school). Consideration needs to be given to the
'sampling frame’ – such as the voting register, telephone book etc. If the sampling frame is
biased, such as richer people being ex-directory or poorer people avoiding the voting
register, then this problem will be reflected in the sample.
2. Non-probability sampling. This can be useful when there is insufficient information about the
population (i.e. there is uncertainty about how many people or events make up the
population) or the population is intrinsically difficult to survey e.g. the homeless. Non
probability sampling techniques include purposive sampling (e.g. the sample is handpicked)
or snowballing (those identified for inclusion in the sample nominate others). Caution must
be taken in generalising from such samples.
3. Stratified sampling. This involves dividing the sampling frame into segments and 'oversampling’
sections of the population. For example, a survey might deliberately over-sample
young people or ethnic minorities in order to ensure that there are sufficient in the sample to
make reliable statistical comparisons. Such samples can be 're-weighted’ to give averages
that are representative of the whole population. Stratified sampling is usually necessary for
sub group analysis.
• Optimum sample size: the sample size needs to be an adequate size, in order to generalise from the
survey's findings. Provided that the sample size is representative of the target population, the larger
the sample size, the more confident you can be that the results are an accurate reflection of the
population as a whole. The key factor is the absolute size of the sample, rather than the proportion of
the population that gets included in the sample. Adequate samples can be estimated from the
expected variation in the major variables of interest, and will therefore depend on the specific
question or hypothesis to be tested. As a general rule of thumb, adequate samples will generally
involve more than 30 events or people. Most market research companies use samples of around
1000-2000. However, other factors to consider when deciding on the sample size include the likely
response rate, the desired level of accuracy, sub-divisions in the data etc. For example, if the survey
seeks to discover not only the general attitude towards an issue, but also that of married men under
40, single parents etc, then a larger sample will be needed. Advice from a statistician or social
researcher will help to ensure that the chosen sample size will yield reliable and relevant data.
• Data collection method: there are a variety of different methods for actually collecting survey data.
Each has pros and cons:
1. self-completion postal questionnaires: this can be expensive and the typically low response
rates, can result is a selection bias and hence doubt in the validity of the findings.
2. face to face interviews: market researchers may approach people in the street, or call at
people’s homes. On other occasions contact will be made in advance by phone or letter.
Response rate is usually higher than for postal surveys but face to face interviews tend to be
more expensive. Decisions will need to be made about whether the interviews are to be
structured, unstructured or partially structured.
3. telephone interviews: these are quicker and cheaper than face to face interviews, but have
the highest non-response rate because people are less inhibited about saying no over the
phone.
Checklist for Designing a Survey or Questionnaire
1. Wording of the questions:
• Style of question should be suited to target group e.g. children or professionals. The table below
provides some alternative styles.
• Respondents should only be required to answer about themselves, not others
• Avoid the use of leading questions
Strategy Survival Guide – Strategy Skills
Page 119