Lecture03 - Todays Schedule Frequency Distributions...

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18 April 2003 Biostatistics 6650--L3 1 Today’s Schedule Frequency Distributions Graphical Summaries Data Quality Control
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18 April 2003 Biostatistics 6650--L3 2 Frequency Distributions Provides a very useful tabular summary of any type of data ordered display of all n sample data values and their frequency often includes the percent of n and the cumulative percent(quantitative or ordinal data) sometimes values are grouped quintiles, quartiles, tertiles evenly spaced histograms customary cutpoints
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18 April 2003 Biostatistics 6650--L3 3 Frequency Distributions Example: Rosner Table 2.8, Birthweight from 100 deliveries. Birth wt(oz) Count % Cum Cnt Cum% 32 1 1.00 1 1.00 58 1 1.00 2 2.00 64 1 1.00 3 3.00 …. 112 3 3.00 51 51.00 …. 161 1 1.00 100 100.00 3262 8744 13150 16107 25050 28960 34740 43100 46780 50823 54140 58440 62799 3262 8744 13150 16107 25050 28960 34740 43100 46780 50823 54140 58440 62799 3262 8744 13150 16107 25050 28960 34740 43100 46780 50823 54140 58440 62799 Total Level 1 1 1 1 1 1 1 1 1 1 1 1 1 13 Count 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 0.07692 1.00000 Prob 0.07692 0.15385 0.23077 0.30769 0.38462 0.46154 0.53846 0.61538 0.69231 0.76923 0.84615 0.92308 1.00000 1.00000 Cum Prob 13 Levels Frequencies md Distributions X ordinal; analyze distribution; click on freq table; select “Cum Prob”
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18 April 2003 Biostatistics 6650--L3 4 Frequency Distributions Frequency Distributions Example Table 1 from paper looking at predictors of biochemical failure after radical prostatectomy PSA, ng/ml No.Pts(% of n=2518) <=4.0 442(18) 4.1-10.0 1170(46) 10.1-20.0 553(22) >20.0 353(14)
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18 April 2003 Biostatistics 6650--L3 5 Graphical Displays of Data Purpose: show the characteristics of the data variability typical values / atypical values (outliers) detect patterns: shapes, number of modes, etc. A picture is worth a 1000 words…. IF it conveys a clear message labels are clear, accurate, meaningful units are indicated free of clutter excellent graphics reference books: Cleveland, William S. The Elements of Graphing Data. Tufte, Edward. The Visual Display of Quantitative Information.
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18 April 2003 Biostatistics 6650--L3 6 Graphical Displays of Data Graphical Displays of Data Graphical Summaries histograms frequency polygons cumulative frequency polygons bar graphs dot plots stem-leaf plots box plots before/after examples of poor graphical summaries
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18 April 2003 Biostatistics 6650--L3 7 Histograms Histogram--graphical display of frequency distribution typically used for numerical attributes(continuous) with n>50 data are divided into a number of groups(intervals) rectangles are constructed such that
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This note was uploaded on 06/17/2011 for the course BME 6650 taught by Professor Multipleinstructors during the Spring '03 term at Mayo Clinic College of Medicine.

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Lecture03 - Todays Schedule Frequency Distributions...

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