Biostatistics by Geoffrey Norman David Streiner & David L. Streiner

Author:Geoffrey Norman,David Streiner & David L. Streiner [Norman]
Language: eng
Format: epub
ISBN: 9781607952794
Publisher: People's Medical Publishing House USA Ltd (PMPH)
Published: 2014-04-11T16:00:00+00:00

CHAPTER THE SEVENTEENTH

Measuring Change

There are a number of approaches to examining the change in a variable over time. The simplest involves difference scores, and is analyzed with a paired t-test. Analysis of covariance is more appropriate, and generally leads to a more powerful test. ANCOVA can also be generalized to the situation in which there are multiple occasions of measurement.

SETTING THE SCENE

Over the years, people with arthritis have fallen prey to countless over-the-counter preparations, guaranteeing immediate relief from the pain, and charging outrageous prices considering that about 90% are just variants on aspirin. In this chapter, we examine one more of the family, Robert's Rectal Pills, which has the dubious advantage that its mode of administration is somewhat unusual, at least for an aspirin concoction. In the course of doing so, we explore a number of methods for assessing change (in this case, change in joint counts) ranging from the simple, obvious, and ubiquitous methods (difference scores and paired t-tests) to more advanced and powerful methods, including ANCOVA.

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