R notes for Activity 25-3: Got a Tip?

We start by creating the table.

CardTips = data.frame(row.names=c("Tip","No Tip"),
  Joke = c(30,42),
  Ad = c(14,60),
  None = c(16,49))

Then we use the chi-square test.

chisq.test(CardTips)

To help ourselves think about the meaning, we build a table of expected values.

ExpectedTips = rowSums(CardTips) %o% colSums(CardTips)/sum(CardTips)

We then compare that table to our original table. (Do you notice anything interesting about the columns?)

CardTips - ExpectedTips

We then see what contributed to the high chi-square value.

(CardTips-ExpectedTips)^2/ExpectedTips