Question

Melanoma treatment. An experiment evaluated the use of genetically engineered white blood cells in the treatment of patients with melanoma.^y Patients were divided into three cohorts. Patient cohort 1 received genetically engineered lymphocytes that were cultured ex vivo for 19 days. Cohort 2 received cells that were cultured for between 6 and 9 days. Cohort 3 received cells that were generated by a second rapid expansion performing after 8 to 9 days. Cell doubling times were as follows.

Cohort 1               8.7          11.9        10.0

Cohort 2               11.4        1.0          1.3          1.0          2.0          0.6          0.8          0.7          0.9          1.9

Cohort 3               0.9          3.3          1.2          1.1

Either create a file with these data or download the file MORGAN2006.* from the companion website. Most statistical programs require you to enter that data into two columns: one column for the explanatory variable (COHORT) and the other for the response variable (DOUBLING). Your final data table should have 2 columns and 18 rows.

If you do not have access to a statistical program, consider using BrightStat. com.^z Use of BrightStat.com is free. However, you must register as a user in order to access its ANOVA features.

(a)   Calculate the means, standard deviations, and sample sizes of each group. Use the “double the standard deviation” benchmark to assess whether group variances are significantly different. Is there evidence of heteroscedasticity?

(b)   Conduct Levene’s test for unequal variance. Show all hypothesis testing steps. What do you conclude?

Answer 1