Application of Multivariate Analysis

#1
The following situation is proven valuable where multivariate analysis can be applied. This example is taken from the book `Applied Multivariate Statistical Analysis` written by `Richard A. Jhonson & Dean W. Wichern`.:

"A study was conducted to investigate the reactions of cancer patients to radiotherapy. Measurements were made on \(6\) reaction variables for \(98\) patients. Because it was difficult to interpret observations on all 6 variables at the same time, a simpler measure of patients response was required. Multivariate analysiswas used to construct a simple measure of patient response to radiotherapy,yet one that still contained much of the available sample information.

The data consist of average ratings over the course of treatment for patients undergoing radiotherapy. Variables measured included: \(x_1\)(symptoms),\(x_2\)(amount of activity),\(x_3\)(amount of sleep),\(x_4\)(amount of food consumed),\(x_5\)(appetite),\(x_6\)(skin reaction)."*

I have not understood how the situation describes the application of multivariate analysis ? As i understood the multivariate analysis is applicable when there are more than one outcome variables which are observed and analysed at the same time.

Where are the several outcome variables in the above described situation ?