To illustrate the two approaches to factor analysis, consider a within-participant experiment that aims to answer the research question, “Which visual form of an image best supports visual search?” The independent variable is the visual form of an image with three conditions: Black and White (BW), Colour (C), and Grey-scale (GS).

Each screen presents forty items, and there is only one task – identify the largest image. To ensure generalisability of the results, there are three experimental objects, each using a different type of image: images of the environment (photographs, P), paintings (photographs of paintings, PP), and graphics (images created using a digital imaging tool, G). Error and response time data are collected, but only error data are analysed here. Data for this experiment (fabricated for the purposes of illustration) are shown in Table A3.1.

The primary independent variable primary independent variable is visual form (BW, C, GS) because this is directly related to the research question. A secondary independent variable is image type (with three secondary conditions, P, PP, G).