Quantitative Medicine Week 1: The Basics

Question 1

Nominal

Answer 1

A nominal variable consists of named categories, with no implied order among the categories.

Question 2

Ordinal

Answer 2

But there could have been only a 1-second difference between the first two horses, with the third trailing by 10 seconds. So letter grades and the order of finishing a race are called ordinal variable

Question 3

Interval

Answer 3

An interval variable has equal distances between values, but the zero point is arbitrary.

Question 4

Ratio

Answer 4

If the zero point is meaningful, then the ratios between numbers are also meaningful, and we are dealing with (not surprisingly) a ratio variable.

Question 5

Proportion

Answer 5

A proportion is a type of fraction in which the numerator is a subset of the denominator. That is, when we write X, we mean that there are three objects, and we’re talking about one of them. Percentages are a form of proportions, where the denominator is jigged to equal 100. This may seem so elementary that you may wonder why we bother to mention it. There are two reasons. First, we’ll later encounter other fractions (e.g., odds) where the numerator is not part of the denominator; and second (here’s where statisticians often screw up), people sometimes call a proportion a “rate.” But, strictly speaking, a rate is a fraction that also has a time component. If we say that 23% of children have blue eyes (a figure we just made up on the spot), that’s a proportion.

Question 6

Rate

Answer 6

if we say that 1 out of every 1,000 people will develop photonumerophobia this year, that’s a rate, because we’re specifying a time interval.