### Solution to question 2.2

The variable *n* is simply the number of subjects in this study group. It is a **discrete metric** variable as it is *countable*.

*dmft* is a **discrete metric** variable (you *count* the number of decayed missing and filled teeth. (Note that it is possible for the mean of a discrete variable to be any value, not just whole numbers.) Similarly *Decayed/filled teeth* and *Extracted teeth* are **discrete metric** variables.

*% caries-free* is a **continuous metric** variable. The value of this variable is infinitely variable (between the values of 0 and 100).

The four social class variables, as presented here look to be **continuous metric** variables (like *% caries-free* above) and, indeed this is how they were treated in the paper. The authors, however, made a mistake. These are not really four *independent* variables but four categories of *one* **nominal** variable, *social class* (or, possibly, four categories of *one* **ordinal** variable, if we choose to regard *social class* in that way.