Percent increase and percent decrease still confuse the heck out of me, no matter how many problems I do or how many times I teach the topic. The language gets
- Has the high school graduation rate of black males increased by 6.6% or 5.1%?
- Has their high school dropout rate decreased by 37.9% or 5.8%?
- Has their college enrollment rate increased by 32.7% or 1.7%?
- Has their incarceration rate decreased by 25.3% or 2.1%?
Two bigger questions:
- Would the positive changes for black males highlighted by this list of statistics still be as powerful if they had cited the change in percentage rather than the percent change (of the percent)? Either way, they still show increases where we would want there to be increases (high school graduation rate, college enrollment, college "by the numbers") and decreases where we would want there to be decreases (dropout rate, "incarcerated").
- In what other ways could this information be presented (pure numbers, different types of graphs, etc.) that would make them more or less powerful? How do you think the author chose this table?
What is the difference between "net increase" and "percent increase"? Is there a difference? How does this very, very subtle difference change how we present and interpret statistics about changes that are measured in and by percents? The Wikipedia article on percents has some interesting things to say, including how the use of the term "percentage points" can help clear up confusion.
As teachers, especially teachers of English Language Learners, how do we support students in navigating this very tricky language. It seems particularly important/frustrating given that percent increase/decrease problems are a not insignificant part of the California High School Exit Exam. (Really, no concept is insignificant when one or two questions could make the difference in whether you earn a high school diploma.)
