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Unformatted text preview: Briggs UTDallas GISC 6382 Spring 2007 1 Spatial Statistics Concepts (O&U Ch. 3) Centrographic Statistics (O&U Ch. 4 p. 7781) – single, summary measures of a spatial distribution Point Pattern Analysis (O&U Ch 4 p. 81114)  pattern analysis; points have no magnitude (“no variable”) Quadrat Analysis Nearest Neighbor Analysis Spatial Autocorrelation (O&U Ch 7 pp. 180205 – One variable The Weights Matrix Join Count Statistic Moran’s I (O&U pp 196201) Geary’s C Ratio (O&U pp 201) General G LISA Correlation and Regression – Two variables Standard Spatial Briggs UTDallas GISC 6382 Spring 2007 2 Description versus Inference • Description and descriptive statistics – Concerned with obtaining summary measures to describe a set of data • Inference and inferential statistics – Concerned with making inferences from samples about populations – Concerned with making legitimate inferences about underlying processes from observed patterns We will be looking at both! Briggs UTDallas GISC 6382 Spring 2007 3 Classic Descriptive Statistics: Univariate Measures of Central Tendency and Dispersion • Central Tendency: single summary measure for one variable: – mean (average) – median (middle value) – mode (most frequently occurring) • Dispersion: measure of spread or variability – Variance – Standard deviation (square root of variance) Formulae for variance 2 ) ( 1 2 ∑ = N X X n i i ] / ) [( 1 2 ∑ = ∑ = N N X X n i i Formulae for mean These may be obtained in ArcGIS by:opening a table, right clicking on column heading, and selecting Statisticsgoing to ArcToolbox>Analysis>Statistics>Summary Statistics Briggs UTDallas GISC 6382 Spring 2007 4 A counting of the frequency with which values occur on a variable • Most easily understood for a categorical variable (e.g. ethnicity) • For a continuous variable, frequency can be: – calculated by dividing the variable into categories or “bins” (e.g income groups) – represented by the proportion of the area under a frequency curve Classic Descriptive Statistics: Univariate Frequency distributions1.96 2.5% 1.96 2.5% In ArcGIS, you may obtain frequency counts on a categorical variable via:ArcToolbox>Analysis>Statistics>Frequency Briggs UTDallas GISC 6382 Spring 2007 5 Classic Descriptive Statistics: Bivariate Pearson Product Moment Correlation Coefficient (r) • Measures the degree of association or strength of the relationship between two continuous variables • Varies on a scale from –1 thru 0 to +11 implies perfect negative association • As values on one variable rise, those on the other fall (price and quantity purchased) 0 implies no association +1 implies perfect positive association • As values rise on one they also rise on the other (house price and income of occupants) X Where Sx and Sy are the standard deviations of X and Y, and X and Y are the means....
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This note was uploaded on 02/15/2012 for the course GEO 6938 taught by Professor Staff during the Summer '08 term at University of Florida.
 Summer '08
 Staff

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