A person wants to compare the average oxygen saturation for two patient groups. Which measurement scale should be used for the data?

In healthcare statistics, comparing averages typically involves measurement scales that allow for meaningful calculations. In this case, the average oxygen saturation represents a continuous variable that follows a true zero point, indicating no oxygen saturation at all. This characteristic suggests the use of a ratio scale, which is ideal for measuring quantities where both differences and ratios are relevant.

A ratio scale not only compares differences between values but also supports the computation of meaningful ratios. For example, an oxygen saturation level of 100% is twice as much as 50%, making it feasible to measure and interpret findings accurately. This level of measurement is essential when considering statistical analyses such as t-tests or ANOVA, which assume that the data meet ratio scale criteria.

In contrast, an interval scale does not have an absolute zero point, which limits the interpretations that can be drawn. Ordinal scales, which rank data without specifying the magnitude of difference between ranks, and nominal scales, which categorize data without any quantitative value, are also insufficient for analyzing average oxygen saturation as they do not allow for meaningful mathematical operations.

Therefore, the ratio scale is the most appropriate choice for comparing the average oxygen saturation levels in this scenario.