ABSTRACT
If, in an undergraduate examination, three students are placed first, second, and third, it is possible to say that a the first student has done better than the second and third. This is an example of ordinal data; this merely means that categorical data can be put into a meaningful order or ranked. It does not indicate that there is a significant difference between the students, by how much the first placed was better than the second, or indeed that any of them passed the examination. In anaesthesia, there is increasing use of scoring systems, e.g. the Malampatti scoring system of airway assessment. The fact that there are four scores (1, 2, 3, and 4) does not mean that a grade 2 is twice as difficult to intubate as grade 1. Another type of discrete data may have a numerical value that is an integer, e.g. ‘three outpatient visits per year’. A frequently used example of discrete numerical data is the number of radioactive counts over a period of time. However, if the count rate is high the data tend to be treated as continuous data. Similarly heart rate, although an example of discrete numerical data (a fraction of a heartbeat is impossible), is similarly treated as continuous data.
