It describes the different ways of summarising continuous data by measures of location or central tendency (mean, median, mode) and measures of spread or variability (range, variance, standard deviation, inter‐quartile range). It also illustrates how to display continuous data (dot‐plots, histograms, box‐and‐whisker plots).
2.1 Types of Data
Just as a farmer gathers and processes a crop, a statistician gathers and processes data. For this reason, the logo for the UK Royal Statistical Society is a sheaf of wheat. Like any farmer who knows instinctively the difference between oats, barley, and wheat, a statistician becomes an expert at discerning different types of data. Sections of this book will refer to different data types and so we start by considering these distinctions. Figure 2.1 shows a basic summary of types, although some data do not fit neatly into these categories.
Figure 2.1 Broad classification of the different types of data with examples.
Example from the Literature – Salicylic Acid Plasters for Treatment of Foot Corns
Table 2.1 gives a typical table reporting baseline characteristics of a set of patients entered into a randomised controlled trial that investigated the effectiveness of salicylic acid plasters compared with usual scalpel debridement for treatment of foot corns (Farndon et al. 2013). Corns and calluses are areas of hard, thickened skin that develop when the skin is exposed to excessive pressure or friction. They commonly occur on the feet and can cause pain and discomfort when you walk. We will discuss the different types of data given in this paper.
Table 2.1 Baseline characteristics of participants in a randomised control trial of the effectiveness of salicylic acid plasters compared with ‘usual’ scalpel debridement of foot corns by treatment group
(Source: Farndon et al. 2013).
| Group | ||||||
|---|---|---|---|---|---|---|
| Corn plaster | Scalpel | |||||
| n | % | n | % | |||
| Gender | Male | 42 | (42%) | 42 | (42%) | |
| Female | 59 | (58%) | 59 | (58%) | ||
| Total | 101 | (100%) | 101 | (100%) | ||
| Centre | Central | 58 | (58%) | 52 | (52%) | |
| Manor | 13 | (13%) | 20 | (20%) | ||
| Jordanthorpe | 10 | (10%) | 14 | (14%) | ||
| Limbrick | 3 | (3%) | 6 | (6%) | ||
| Firth Park | 7 | (7%) | 4 | (4%) | ||
| Huddersfield | 5 | (4%) | 4 | (4%) | ||
| Darnall | 5 | (5%) | 1 | (1%) | ||
| Total | 101 | (100%) | 101 | (100%) | ||
| Smoking History | Non‐Smoker | 34 | (35%) | 40 | (40%) | |
| Previous Smoker | 22 | (22%) | 16 | (16%) | ||
| Current Smoker | 42 | (43%) | 43 | (43%) | ||
| Missing | 3 | (3%) | 2 | (2%) | ||
| Total | 101 | (100%) | 101 | (100%) | ||
| Number of corns evaluated | 1 | 48 | (48%) | 66 | (65%) | |
| 2 | 28 | (28%) | 23 | (23%) | ||
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