Читать книгу Interpreting and Using Statistics in Psychological Research - Andrew N. Christopher - Страница 44

An ordinal scale is a measurement that identifies people, objects, or events in categories, and the categories are ranked in order of their magnitude (e.g., from best to worst). For instance, here are five different vegetables: broccoli, asparagus, green beans, carrots, and red peppers.

You ask me to put them in the order of my preference, with “5” for my most preferred and “1” for my least preferred. Here is my order of preference:

 5 = red peppers

 4 = asparagus

 3 = carrots

 2 = green beans

 1 = broccoli

Each vegetable is identified by a number, which conveys magnitude, that is, how many vegetables are preferred to a specified other vegetable (e.g., relative to green beans, I like carrots, asparagus, and red peppers more, but I don’t like broccoli as much).

Photo 2.3 Putting these vegetables in “order” gives you “ordinal” data.

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Ordinal scale: ranked-ordered data.

The rule for assigning numbers on an ordinal scale is that the position (rank order) of numbers on the scale must represent the rank order of the psychological attributes of the objects or events. Here, those psychological attributes are my liking of each vegetable. Notice that the scale does not tell us how much more I prefer red peppers to asparagus. It gives only the order of preference, not the difference in degree of preference. This is a major limitation of ordinal data. My preference for carrots over green beans may be fairly small, but my preference for green beans over broccoli may be quite large.

With ordinal data, we can calculate certain statistics, such as the mode or median, and perform what is called the Spearman rank-order correlation and the Mann–Whitney U test to help us make sense of this type of data. We will learn how to use such tools in Chapters 3, 4, and 15.