The National Center for Charitable Statistics estimates that individual giving in the United States in 2014 was $258.51 billion. A study to determine who gave and how much they gave was undertaken. A random sample of individuals who gave to charities was drawn. For each respondent, the study recorded the total adjusted gross income (AGI) category and the charitable giving as a percentage of AGI. The AGI categories are listed next. In this study, only individuals whose AGI was between $45,000 and $100,000 were included.

$45,000 to $49,999

$50,000 to $54,999

$55,000 to $59,999

$60,000 to $74,999

$75,000 to $100,000

a. Is there sufficient evidence to conclude that there are differences between the five AGI categories?

b. If differences exist use Tukey’s method to determine which groups differ.