Exam 13: Glm 2: Comparing Means Adjusted for Other Predictors Analysis of Covariance

Which of the following is not considered to be an assumption of ANCOVA?

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 when controlling for the grade of the exam. What analysis should he use?

Consider the graph below. This is the graph of the results of an experimental learning condition as the independent variable and IQ as the covariate. What does the graph indicate?

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 when controlling for the grade of the exam. The first part of the SPSS output is below. What does this part of the output tell us?

To 'partial out' means to

The following scatterplot represents the results of a study undertaken by Chakrabarty et al. (2005) who were investigating glutamate levels in psychotropic drug-naive OCD patients and comparing them with psychiatrically normal controls. Based on this scatterplot the following ANCOVA of glutamate levels in CSF was done. Findings were reported as follows for CSF glutamate levels in OCD patients compared to controls: F(1,29)=11.153, p=0.002. What conclusion can be drawn about this result? Scatterplot showing CSF glutamate levels in patients (1) and controls (2). ANCOVA of Glutamate Levels in CSF Diagnosis (OCD vs Controls) and gender were included as factors, while age, number of years of illness, total Y-BOCS scores, and CGI-S scores were included as covariates in the analysis.

What makes ANCOVA different from ANOVA?

A scatterplot and a summary table for the ANCOVA on the data relating to it are given below. What does the interaction term suggest?

What is not true of the ANCOVA procedure in SPSS?

When assumptions are violated in ANCOVA, which non-parametric test can be carried out?

A health psychologist was interested in the effects of smoking on the suppression of the immune system. Three groups of adults were exposed (in a highly ethical way) to either a cold virus, a flu virus or were left freezing wet in the outside in the middle of winter to catch pneumonia (no more than smokers deserve!). The severity of the disease was then measured as a percentage (0% = not contracted, 100% = contracted to a very severe degree). The psychologist also measured the number of cigarettes that each person smoked per day. The psychologist was interested in the differences in the severity of the three illnesses and the impact of cigarette usage. What technique should be used to analyse these data?

The following scatterplot represents the results of a study undertaken by Chakrabarty et al. (2005) who were investigating glutamate levels in psychotropic drug-naive OCD patients and comparing them with psychiatrically normal controls. Findings were reported as follows for CSF glutamate levels in OCD patients compared to controls: F(1,29)=11.153, p = 0.002. How would these findings be interpreted? Scatterplot showing CSF glutamate levels in patients (1) and controls (2).

In an ANCOVA with one covariate and one independent variable, what null hypothesis is not tested?

Using the SPSS output below, which of the following statements best reflects the effect of 'Grade'?

What is an alternative way to model the design of an ANCOVA?

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 when controlling for the grade of the exam. The second part of the SPSS output is below. Which of the following statements best reflects the effect of 'Instru'?

What does ANCOVA allow the researcher to do with data?

What assumption does ANCOVA have that ANOVA does not?

Adjusted group means are

What does the effect size measure in ANCOVA?