The Essentials of Biostatistics for Physicians, Nurses, and Clinicians

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The Essentials of Biostatistics for Physicians, Nurses, and Clinicians,

First Edition. Michael R. Chernick.

© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

Chapter 1

1. What is a Kaplan – Meier curve?
   A Kaplan – Meier curve is an estimate of cumulative survival over time based on
   possibly right - censored time - to - event data. It is an estimate obtained without
   making a parametric assumption about the shape of the survival curve.


2. Why is randomization important in clinical trials?
   In clinical trials, we are comparing two or more treatments. Confounding can occur
   when the subjects in one treatment group has very different characteristics than the
   other. In one case, there may be a much higher percentage of males in one group
   than in the other, or one group might tend to have older patients than the other. In
   such situations, a signifi cant difference in response between the two groups could
   be due to the difference in treatment, but it also could be due to differences in ages
   or gender. Randomization tends to balance out these factors, thus eliminating the
   confounding.


3. What are retrospective studies?
   Retrospective studies are any type of study where all the data were generated in the
   past and are now being used for the purpose of an investigation that was not con-
   sidered prior to the collection of data.


4. What are controlled clinical trials and why is blinding important?
   In clinical trials, we are comparing two or more treatments on human subjects. The
   trial is considered controlled when randomization is properly used and blinding is

Solutions to Selected Exercises

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