Students tend to assume that all measures produce ratio scale numbers. To show that some measurements may be less than ratio level and to show the implications of this fact, go over handout 6.2, box 6.1, tables 6.1, 6.2, and 6.3.
For a lighter look at scales of measurement, you could use the "scales of measurement as represented by different rulers" handout. For an even lighter look, you could introduce this ruler tattoo and ask students to describe what changes in this person's body or tattoo would result in it no longer producing ratio measurement and instead producing only (a) ordinal (or worse) measurements, (b) interval (or worse) measurements, and (c) nominal measurements.
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