# Mr. David O. Nwafor

Topics: Median, Histogram, Standard deviation Pages: 15 (4943 words) Published: May 1, 2013
Statistical Concepts Series

Describing Data: Statistical and Graphical Methods1
An important step in any analysis is to describe the data by using descriptive and graphic methods. The author provides an approach to the most commonly used numeric and graphic methods for describing data. Methods are presented for summarizing data numerically, including presentation of data in tables and calculation of statistics for central tendency, variability, and distribution. Methods are also presented for displaying data graphically, including line graphs, bar graphs, histograms, and frequency polygons. The description and graphing of study data result in better analysis and presentation of data. ©

Index terms: Data analysis Statistical analysis Published online before print 10.1148/radiol.2253012154 Radiology 2002; 225:622– 628 1

From the Department of Surgery, University of Michigan Medical Center, Ann Arbor. Received January 14, 2002; revision requested March 2; revision received May 20; accepted June 14. Address correspondence to the author, Department of Surgery, University of Pennsylvania Health System, 4 Silverstein, 3400 Spruce St, Philadelphia, PA 19104-4283 (e-mail: seema.sonnad@uphs .upenn.edu). RSNA, 2002

RSNA, 2002

DESCRIPTIVE STATISTICS Frequency Tables
One of the steps in organizing a set of numbers is counting how often each value occurs. An example would be to look at diagnosed prostate cancers and count how often in a 2-year period cancer is diagnosed as stage A, B, C, or D. For example, of 236 diagnosed cancers, 186 might be stage A, 42 stage B, six stage C, and two stage D. Because it is easier to understand these numbers if they are presented as percentages, we say 78.8% (186 of 236) are stage A, 17.8% (42 of 236) are stage B, 2.5% (six of 236) are stage C, and 0.9% (two of 236) are stage...