Final answer:
A z-score is used to compare values from different datasets with different units, such as inches and pounds, because it is a dimensionless number representing the distance from the mean in terms of standard deviations.
Step-by-step explanation:
The question asks which statistical tool can be used to compare values measured in different units, such as inches and pounds. The correct answer is z-score, which is a measure of how many standard deviations an element is from the mean. A z-score can be used to compare different units because it is dimensionless; it translates different units into a common scale of standard deviations away from the mean.
When choosing appropriate units for measurements such as distance, weight, length, and volume, one needs to consider the scale and precision required. For example, distances can be measured in kilometers or miles, weights in grams or pounds, lengths in centimeters or inches, and volumes in milliliters or fluid ounces, depending on whether you are using metric or customary units.