What is 'typical' for different kinds of data?

There are five words that are critical to an appreciation of what is ‘typical’ in data sets that students encounter across the middle school years. The first three words—mean, median and mode—are nouns that define measures of typicality in data sets. The next two words—categorical and numerical—are adjectives that describe the types of data sets to which we may wish to apply the measures. The purpose of this article is to present and discuss in a down-to-earth fashion, with authentic data sets, the relationship of the three measures of typicality and the two types of data introduced in the curriculum. Although the mean, median and mode have been in mathematics text books for many years it is sobering to read in the research literature that teachers’ understanding of the measures is little different from that of students and both struggle (Jacobbe & Carvalho, 2011).