Biostatistics

8.6 SUMMARY 373
Percent Change in CD4 T Cell Treatment Plasma
77.30 1 1
0:44 1 1
50.20 1 1
48.60 2 2
86.20 2 2
205.80 1 2
100.00 1 2
34.30 1 2
82.40 1 2
118.30 1 2
Source: Data provided courtesy of Simona Porcellini, Guiliana Vallanti,
Silvia Nozza, Guido Poli, Adriano Lazzarin, Guiseppe Tabussi,
and Antonio Grassia, “Improved Thymopoietic Potential in Aviremic
HIV Infected Individuals with HAART by Intermittent IL-2
Administration,” AIDS, 17 (2003), 1621–1630.
8.5.5. A study by Gorecka et al. (A-26) assessed the manner in which among middle-aged smokers the
diagnosis of airflow limitation (AL) combined with advice to stop smoking influences the smoking
cessation rate. Their concerns were whether having AL, whether the subject successfully quit
smoking, and whether interaction between AL and smoking status were significant factors in regard
to baseline variables and lung capacity variables at the end of the study. Some of the variables of
interest were previous years of smoking (pack years), age at which subject first began smoking,
forced expiratory volume in one second ðFEV 1 Þ, and forced vital capacity (FVC). There were 368
subjects in the study. What are the factors in this study? At how many levels does each occur? Who
are the subjects? What is (are) the response variable(s)? Can you think of any extraneous variables
whose effects are included in the error term?
8.5.6. A study by Meltzer et al. (A-27) examined the response to 5 mg desloratadine, an H1-receptor
antagonist, in patients with seasonal allergies. During the fall allergy season, 172 subjects were
randomly assigned to receive treatments of desloratadine and 172 were randomly assigned to receive
a placebo. Subjects took the medication for 2 weeks after which changes in the nasal symptom score
were calculated. A significant reduction was noticed in the treatment group compared to the placebo
group, but gender was not a significant factor. What are the factors in the study? At how many levels
does each occur? What is the response variable?
8.6 SUMMARY
The purpose of this chapter is to introduce the student to the basic ideas and techniques of
analysis of variance. Two experimental designs, the completely randomized and the
randomized complete block, are discussed in considerable detail. In addition, the concept
of repeated measures designs and a factorial experiment as used with the completely
randomized design are introduced. Individuals who wish to pursue further any aspect of
analysis of variance will find the methodology references at the end of the chapter most
helpful.