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

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?

What does the relationship of the data in the following scatterplot 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 SPSS output below shows the final tables. Which of the following statements best reflects what these tables tells us?

In a study of favourable effects of berry consumption on platelet formation, blood pressure and HDL cholesterol, the following results are reported Berry consumption inhibited platelet function as measured with a platelet function analyzer (using collagen and ADP as platelet activator) [changes: 11% and -1.4% in the berry and control groups, respectively; P=0.018, ANCOVA]. Plasma biomarkers of platelet activation, coagulation and fibrinolysis did not change during the intervention. Serum HDL-cholesterol concentrations increased significantly more (P=0.006, ANCOVA) in the berry than in the control group (5.2% and 0.6%, respectively), but total cholesterol and triacylglycerol remained unchanged. Systolic BP decreased significantly (P=0.050, ANCOVA). Polyphenol and vitamin C concentrations in plasma increased, whereas other nutritional biomarkers (i.e. folate, tocopherols, sodium and potassium) were unaffected. Source: Erlund, I., Koli, R., Marniemi, J., Puuka, P., Mustonen, P. Mattila, P. & Jula, A. (2008). Favourable effects of berry consumption on platelet function, blood pressure and HDL cholesterol. American Journal of Clinical Nutrition, 87(2). 323-331. Which of the following would you consider a possible conclusion from this report?

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