Читать книгу Medical Statistics - David Machin - Страница 30

If there are more than two categories of classification it may be possible to order them in some way. For example, after treatment a patient may be either improved, the same or worse. In Table 2.1 smoking history is given in three categories: non‐smoker, previous smoker, and current smoker. Thus, someone who is a current smoker has more recent exposure to tobacco than someone who is an ex‐smoker and someone who has never smoked. However, without further knowledge (of the current and past levels of tobacco consumption) it would be wrong to ascribe a numerical quantity to the category, for example, non‐smoker = 0; previous smoker = 1; current smoker = 2, as one cannot say that someone who is a current smoker has twice the levels of tobacco consumption as someone who is a previous smoker. This type of data is also known as ordered categorical or ordinal data.