A variable is any characteristic that is recorded for subjects in astudy.A variable is called categorical if each observations belongs toone of a set of categories.A variable is called quantitative if observations on it take numer-ical values that represent different magnitudes of the variable.1A quantitative variable is called discrete if its possible valuesform a set of separate numbers, such as 0,1,2,3,....,A quantitative variable is continuous if its possible values forman interval.In practice, the method of data analysis depends on the type ofvariable.2Frequency TablesEach observation falls in one of several categories.A frequency table is a table that summarizes the number ofobservations in each category.The category with the highest frequency is called the mode.Students in this class (who declared a political allegiance):Party Frequency Proportion PercentageDemocrat 35 0.515 51.5%Independent 12 0.176 17.6%Republican 21 0.309 30.9%Total 68 1.000 100%3The proportion of observations that fall in a certain category isthe frequency (count) of observations in that category dividedby the total number of observations. The percentage is theproportion multiplied by 100. Proportions and percentages arealso called relative frequencies.4Describing Data Using GraphicalSummaries1. Categorical Data2. Quantitative Data5Graphs for Categorical Variables• Pie charts• Bar graphs6Pie chart7Bar graph8Segmented bar graph9Segmented bar graph expressed as percentages10Graphs for Continuous Variables• Dot Plots• Stem and Leaf Plots• Histograms11Heights of students in this class:76 64 66 63 63 63 70 70 67 6870 67 62 70 63 68 65 72 64 6471 67 63 63 68 67 68 64 69 6266 65 66 63 65 63 64 68 70 6366 64 77 66 61 74 68 68 63 6361 62 68 61 68 67 60 66 69 7063 73 72 61 66 70 62 72 70 656212Dot Plot**** ** * ** * * ** * * * ** * * * * * ** * * * * * * * ** * * * * * * * * ** * * * * * * * * * ** * * * * * * * * * * * * * * * *60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 7713Stem and Leaf Plot (first attempt - worst)6 | 01111222223333333333334444445555666666677777888888888997 | 000000001222346714Stem and Leaf Plot (second attempt - better)6 | 01111222223333333333334444446 | 5555666666677777888888888997 | 000000001222347 | 6715Stem and Leaf Plot (third attempt - best)6 | 011116 | 222223333333333336 | 44444455556 | 6666666777776 | 888888888997 | 0000000017 | 22237 | 47 | 6716Histogram with bin width 317Histogram with bin width 218Histogram with bin width
View Full Document
Unlocking...