Multiple choice questions

What assumption does ANCOVA have that ANOVA does not?

A. Homogeneity of variance
B. Homoscedasticity
C. Homogeneity of sample size
D. Homogeneity of regression slopes

A music teacher had noticed that some students went to pieces during exams. He wanted to test whether this performance anxiety was different for people playing different instruments. He took groups of guitarists, drummers and pianists (variable = ‘Instru’) and measured their anxiety (variable  = ‘Anxiety’) during the exam. He also noted the type of exam they were performing (in the UK, musical instrument exams are known as ‘grades’ and range from 1 to 8). He wanted to see whether the type of instrument played affected performance anxiety while accounting for the grade of the exam. What analysis should he use?

1. Independent analysis of variance
2. Repeated measures analysis of variance
3. Analysis of covariance
4. Mixed analysis of variance

A health psychologist was interested in the effects of vitamin supplements on the immune system. Three groups of adults were exposed (in a highly ethical way) to the cold virus; one group took no supplements for a week before exposure, another had vitamin C supplements, and a third had multivitamins (excluding C). The severity of the cold was measured as a percentage (0% = not contracted, 100% = very severe symptoms). The psychologist also measured the number of cigarettes that each person smoked per day, as smoking suppresses the immune system. The psychologist was interested in the differences in the severity of the illnesses across different vitamin groups accounting for cigarette usage. What technique should be used to analyse these data?

1. Two-way repeated-measures ANOVA
2. Two-way independent ANOVA
3. One-way analysis of covariance
4. Two-way mixed ANOVA

ANCOVA is:

1. Used to correct for unmeasured variables that could affect the outcome variable.
2. Is a method of portioning the results of ANOVAs to investigate where differences between independent variables lie.
3. Is a robust version of ANOVA.
4. An extension of ANOVA that partials out the effect of other measured variables.

Answer: An extension of ANOVA that partials out the effect of other measured variables

Which of the following are affected by including a covariate in an analysis of variance?