Rating Spatial Brightness: Does The Number Of Response Categories Matter?

Category rating is a procedure for measuring population opinion or evaluation. Many previous studies have used category rating to evaluate spatial brightness and other aspects of the visual environment in order to compare the effectiveness of different lighting conditions such as the spectral power distribution of the light source. There are suggestions in the literature that the number of response categories in a semantic differential rating scale can affect judgements. For example, Dawes’ study found that mean ratings of price consciousness were different when recorded with response scales of either 5, 7 or 10 categories. A key question is whether or not the response range should include a neutral (or, middle) category, i.e. an odd or even number of response categories. There is evidence that the presence of neutral categories can enhance response contraction bias and this reduces ability to discriminate between stimuli. However, scale format has not been extensively examined for appraisals of the visual environment. Evaluations were carried out using response ranges of 5, 6, 7 or 8 categories. A range of graphical and statistical methods of analysis were employed, with one approach being to ignore all ratings given to the neutral category in odd scales. It was found that while the response distribution may have changed, the number of response categories did not affect the central tendency of opinion.