Simmons - calculating the index

Lots of students have been asking about the numerator/denominator question on the latest Simmons assignment. Lucky for us, the librarians at the University of Georgia explain the calculation on this site.

Here's the quote: "The index of 139 expresses the likelihood of females who bought Nike sneakers to be in this age group, when compared to all females who bought Nike sneakers, a base index of 100. The index was computed by dividing 27.0 (the horizontal % in the Nike column) by 19.4 (the horizontal % in the cell above it) and multiplying by 100. Females in this age group are 39% (139 minus 100) more likely than all female adults to have bought Nike sneakers. Note that the buyers of Reebok in the column to the right have an index of 69, which means that 18-24 year olds are 31% (100 minus 69) less likely than all females to buy that brand." (from Simmons Study of Media and Markets: A Basic Tutorial).

Thank you, Matt, for finding this excellent tutorial just in time!

Thank you, librarians in Georgia!