In Exercises 21-28,determine which of the four levels of measurement (nominal, ordinal, interval, ratio) is most appropriate.

Lead in Blood: Blood lead levels of low, medium, and high used to describe the subjects in Data Set 7 “IQ and Lead” in Appendix B.

The level of blood lead is measured at three levels (low, medium, and high).

There are four different levels of measurement:

• Nominal: Data that is used to represent qualitative and discrete variables is measured under a nominal level.
• Ordinal: Data that occurs in a natural order but the amount of difference between the orders cannot be quantified come under an ordinal level of measurement.
• Interval: Data for which differences can be calculated are measured under an interval scale. The ratios of these values have no meaning.
• Ratio: Data that has an absolute zero value apart from all other properties of the remaining three scales is measured under the ratio scale.

Since blood lead levels (low, medium, and high) follow an order, but the difference between them is not known, so they follow anordinal level of measurement.