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4. Ratio Data

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About this Lecture

Lecture

In this lecture, we think about ratio data and scales, focusing in particular on: (i) the importance of zero meaning something (nothing in this case) in ratio scales; (ii) the role that measurement units have in ratio scales, meaning that the scale can be validly represented in a variety of ways; (iii) the key notion that, irrespective of the measurement unit used, the difference between value points is always the same ratio; (iv) the history of measurement pre-Steven’s measurement levels, which indicated that ratio measurement was understood simply as measurement; (v) the notion that everything which is true of a ‘lower’ measurement scale is true of a ‘higher’ one.

Course

In this course, Professor Dominic Dwyer (Cardiff University) explores measurement levels and scales. In the first lecture, we think about the origin of measurement scales in psychology, and the role of Stanley Smith Stevens in establishing the four measurement levels: nominal, ordinal, interval, and ratio. In the second lecture, we think about nominal scales and their prevalence in behavioural genetics, despite statistical limitations. In the third lecture, we think about ordinal scales and their regular use in survey data collection. Next, we think about ratio scales and the importance of zero meaning something (nothing) in these scales. In the fifth lecture, we think about interval scales and their lack of applicability to ratios of data, due to the arbitrary nature of the zero value. In the sixth and final lecture, we think about how these measurement scales can be summarised and discuss some of the challenges to Stevens’ understanding of measurement.

Lecturer

Professor Dominic Dwyer is the chair for the BSc and MSc exam boards in the School of Psychology at Cardiff University. Professor Dwyer teaches introductory statistics for undergraduate years one and two. Professor Dwyer’s research is primarily focused on how animals and people learn, as well as how that learning is expressed as behaviour. Some key focus areas of this research are computational modelling, neurodegenerative disorders, and the assessment of individual differences. Some of Professor Dwyer’s recent publications include 'EXPRESS: Instrumental responses and Pavlovian stimuli as temporal referents in a peak procedure' (2022) and 'Face masks have emotion-dependent dissociable effects on accuracy and confidence in identifying facial expressions of emotion' (2022).