UNC-Chapel Hill GEOG 070 - Simple Descriptive Statistics (31 pages)

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Simple Descriptive Statistics



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Simple Descriptive Statistics

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Lecture Notes


Pages:
31
School:
University of North Carolina at Chapel Hill
Course:
Geog 070 -

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Simple Descriptive Statistics Descriptive statistics provide an organization and summary of a dataset A small number of summary measures replaces the entirety of a dataset You re likely already familiar with some simple descriptive summary measures 1 2 3 4 5 Ratios Proportions Percentages Rates of Change Location Quotients David Tenenbaum GEOG 070 UNC CH Spring 2005 Simple Descriptive Summary Measures 1 Ratios of observations in A of observations in B e g A 6 overcast B 24 mostly cloudy days 2 Proportions Relates one part or category of data to the entire set of observations e g a box of marbles that contains 4 yellow 6 red 5 blue and 2 green gives a yellow proportion of 4 17 or acolor yellow red blue green ai proportion acount 4 6 5 2 ai David Tenenbaum GEOG 070 UNC CH Spring 2005 Simple Descriptive Summary Measures 2 Proportions cont Sum of all proportions 1 These are useful for comparing two sets of data w different sizes and category counts e g a different box of marbles gives a yellow proportion of 2 23 and in order for this to be a reasonable comparison we need to know the totals for both samples 3 Percentages Calculated by proportions x 100 e g 2 23 8 696 use of these should be restricted to larger sample sizes perhaps 20 observations David Tenenbaum GEOG 070 UNC CH Spring 2005 Simple Descriptive Summary Measures 4 Rates of Change Expressing the change in a variable with respect to its original value e g x t2 x t1 change in x Z x t1 original value of x e g if we had 20 marbles and then added 10 the rate of change 30 20 20 10 20 0 5 5 Location Quotients An index of relative concentration in space a comparison of a region s share of something to the total David Tenenbaum GEOG 070 UNC CH Spring 2005 Simple Descriptive Summary Measures 5 Location Quotients cont For example suppose we have a region of 1000 km2 which we subdivide into three smaller areas of 200 300 and 500 km2 respectively labeled A B and C The region has an influenza outbreak with 150 cases in the



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