5. Interval Data

About this Lecture

Lecture

In this lecture, we think about interval data and scales, focusing in particular on: (i) the lack of a zero, meaning nothing, in the interval scale; (ii) the example of Celsius and Fahrenheit temperature scales as illustrations of interval data; (iii) the outcome of an arbitrary zero manifesting as the interval values remaining the same between two points on each scale, but the ratios of those values being different; (iv) the importance of matching the properties of specific data types to the properties of each measurement scale, in order to assess the best one to use; (v) the maintained applicability of the mode, median, mean, and standard deviation in interval data, despite its lack of ratio representation.

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).