Introduction to Statistical Methods Session 3 Univariate Data Daniel D Reidpath 28 June 2011 Kinds of statistics Location Spread Mean, 25th percentile, Mode Range, variance, standard deviation Shape Uniform, “Normal” Interrelationship/Difference Fit Kinds of Data Ratio data Interval data 2Y is twice as big as Y The difference between Y+2 and Y+5 is 3 Ordinal data Sometimes treated as truly ordered data Sometimes treated as a “Factor” Sometimes treated as interval or even ratio (*sigh*) Kinds of Data... Nominal Factors Groups Binary/Dichtomous Logical (True/False) Nominal Missing Nominal Data • In general the numerical descriptions for nominal data are • Frequencies – counts • Percentages or Proportions • The common visual plot for nominal data is the barchart (or in R .. The barplot() ) • Load Session3.R and have a look at the Titanic Data Ordinal Data • Numerical Descriptions for ordinal data include medians, range and quartile range • The typical plot is the boxplot. • Using Session3.R, have a look at the famous Iris data from RA Fisher. Photograph by Eric Guinther Continuous Data • Common summary descriptions for data involve some kind of central point measure, and some measure of variation. • What would be good for continuous data?