Sample size during
Two questions frequently arise when data collection is being planned:
- How many users should I observe/ get data from? Is the effect
I have found statistically reliable?
- The use of power analysis enables the researcher to get
a handle on both these questions.
The size of the sample, the statistical power of the measuring
instrument, and the size of the effect being investigated are three
inter-linked issues. Estimating the Cost of Quantitative Evaluation
is paper on the HFRG resources page which gives an overview of the
concepts involved, and suggests definitions of various effect
sizes in HCI: known as small, medium, and large effects.