A study of drug addicts in Amsterdam recorded how often each addict had recently injected drugs and whether or not the addict was infected with HIV, the virus that causes AIDS. Here is a two-way table of the numbers of addicts in each condition:

The chi-square statistic for this table has how many degrees of freedom?
A) 1
B) 2
C) 3
D) 4
E) 6

Question

A study of drug addicts in Amsterdam recorded how often each addict had recently injected drugs and whether or not the addict was infected with HIV, the virus that causes AIDS. Here is a two-way table of the numbers of addicts in each condition:

The chi-square statistic for this table has how many degrees of freedom?

The chi-square statistic for this table has how many degrees of freedom?
A) 1 
B) 2 
C) 3 
D) 4 
E) 6

Quizplus · Accepted Answer

The chi-square statistic for this table requires calculating the expected frequencies assuming that there is no association between drug use and HIV infection, and then comparing them to the observed frequencies. The degrees of freedom for a two-way table are (number of rows - 1) times (number of columns - 1), so in this case it is (2-1) times (2-1) = 1. Therefore, the chi-square statistic has 1 degree of freedom.

A Study of Drug Addicts in Amsterdam Recorded How Often