Skip to main content

Access and sampling issues

Chapters 9 & 13

  • Who do you need to study in order to investigate your research questions?
  • How easily can you gain access to a sampling frame?
    • You need to confirm at the earliest opportunity that you have the necessary permission to conduct your work. This is sometimes a prerequisite of ethical approval.
    • (Also see page 209)
  • What kind of sampling strategy will you employ?
    • e.g. probability sampling, quota sampling, theoretical sampling, convenience sampling
  • Can you justify your choice of sampling method?
  • How will you select your sample size?
    • With small or targeted samples, how have you selected your participants?
    • (Also see pages 195-197, 397-399)

Sample Size and Confidence Interval Calculators: - from Raosoft - from Creative Research Systems

To see video clips of students talking about access and sampling issues, click here

Exercise: sample size



Suggest an appropriate sample size to measure a population with respect to the percentage of persons owing two cars in a family in Huddersfield. We may have a rough idea of the likely percentage and wish to sample to be accurate within 5% points and to be 95% confident of this accuracy.

Generally for percentages, sample size may be calculated using the formula:



n = sample number

n = estimate proportion

q = non-estimated proportion

SE = standard error of percentage

Consider the standard error of a percentage.


Assume we guess that the percentage ownership of two car families is 30%

Then standard error of a percentage is:


But 2 (SE(p)) must equal 5% (the level of accuracy required)







Sample size = 336

Check your answer