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

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). Source: http:/ / www.nature.com/ npp/ journal/ v30/ n9/ full/ 1300733a.html

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 SPSS output below shows the final tables. Which of the following statements best reflects what these tables tells us?

Adjusted group means are

Under what circumstances would you not consider using analysis of covariance?

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

In an experiment to study the effectiveness of three different teaching programmes on children's achievement in mathematics, what might not be an appropriate covariate?

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

A scatterplot and a summary table for the ANCOVA on the data relating to it are given below. What does the interaction term suggest? Source: http:/ / www-personal.umich.edu/ ~kwelch/ 510/ 2008/ handouts/ spss_ancova.doc

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 the effect size measure in ANCOVA?

What is not true of the ANCOVA procedure in SPSS?

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. What analysis should he use?

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?

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). Source: http:/ / www.nature.com/ npp/ journal/ v30/ n9/ full/ 1300733a.html 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. Source: http:/ / www.nature.com/ npp/ journal/ v30/ n9/ full/ 1300733a.html

What assumption does ANCOVA have that ANOVA does not?

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

What makes ANCOVA different from ANOVA?

What does ANCOVA allow the researcher to do with data?