LabMasters is doing early safety testing of a new medication

LabMasters is doing early safety testing of a new medication intended to fight Castleman disease. Before doing any human testing, it is using two species of mouse: Peromyscus leucopus and Peromyscus maniculatus. It has tested no dose, a low dose, and a high dose of the new medication on various mice. It used 8 mice overall for testing.

LabMasters has measured the number of days – with a maximum of 40 – that each mouse lived after being administered the drug (or the study beginning, in the case of no dose). There could be trouble with the drug if any of the dosage amounts (including no dose) affects the rodents’ survival times compared to the other dosages.

LabMasters plans to run two-way (factorial) analysis of variance, with interactions.

Suppose that the sums of squares are 50 between treatments, 40 between blocks, and 400 overall.

What is the number of degrees of freedom for interactions?

A. 1

B. 2

C. 3

D. 6

Solution

Here blocks are 2, as 2 species of mouse so Dr of block is 1. Treatments are 3, no, low and high dose, so it\'s df is 2.

Interaction is block x treatment. So df of interaction is df of treatment x df of block=2x1=2. Ans is b 2.