Before Jonas Salk discovered a vaccine to prevent polio, people noticed a correlation between outside temperature and the incide
nce of polio: The warmer the temperature over the course of the year, the more outbreaks of polio. This relationship is an example of a(n) ________ correlation.
Positive correlations mean that two variables are directly proportonal (they move in the same direction). In the example, the correlation is positive because more warmth = more outbreaks of polio.
In other words, positive correlations involve "more = more" or "less = less" relationships.
