Chapter 3 Visual Display of Data

Frequency Tables Binning Data Class Freq 0-9 2 10-19 5 20-29 7 Grouping/categorizing data Each bin(group) covering a range of the possible data values Class Freq 0-9 2 10-19 5 20-29 7 30 or more 6 Total 20

Relative Frequency The proportion or percentage of the data values that fall in that category(group) Grade Freq Relative Freq A 4 0.16 B 7 0.28 C 9 0.36 D 3 0.12 E 2 0.08 Total 25 1.00

Cumulative Frequency The number of data in that category(group) and all preceding categories Grade Freq Cum. Freq A 4 B 7 11 C 9 20 D 3 23 E 2 25 Total

Exercise Exercises with Excel

Picturing Distributions of Data The way values are spread over all possible values. Summarizes with table or graph

Graphs Title/Caption Vertical Scale & Title Horizontal Scale & Title Legend Bar graphs Bars representing frequencies (or relative frequencies) for particular categories. Bar lengths are proportional to the frequencies Dotplots Data value is represented with dot Pareto Charts A bar graph with bars arranged in freq order. Only make sense for data at the nominal level measurement

Graphs (cont.) Pie Charts Histograms A circle divided so that each wedge represents the relative frequency of a particular category Histograms A bar graph showing a distribution for quantitative data (at the interval or ratio level of measurement) The bars have a natural order and the bar widths have specific meaning

Graphs (cont.) Stem-and-leaf plot Line Charts (Frequency Polygon) Like a histogram turned sideways A listing of the individual data sources or values instead of bars Line Charts (Frequency Polygon) A distribution of quantitative data as a series of dots connected by lines. For each dot, the horizontal position is the center of the bin it represents and the vertical position is the frequency value of the bin

Graphs (cont.) Time-Series Diagrams A histogram or line chart in which the horizontal axis represents time

Exercise MS Excel

Graphics in the Media Multiple Bar graphs and Line Charts Stack Plots Multiple sets of data displayed on the same chart for comparison purpose Stack Plots Multiple sets of data stacked (as columns) Geographical Data Contour map Three-Dimensional Graphics Complex Graphics

Exercises Ex17-19 pp123-124 (MS Excel)

A few cautions about graphics Perceptual Distortions Length, height, area, volume Watch the scales Uniform/non-uniform scale Stretched/compressed scale Unadjusted Economic Data Effect of inflation The real cost

A few cautions about graphics (cont.) Percentage change graphs Downward-sloping lines show that the rate of percentage increase slowed, not that the actual value went down Pictographs More appealing But can also distract or misled

Focus on Environment How Can We Visualize Global Warming? pp140-142