Oct 1 2002 Lecture 2 Econ240A 1 Exploratory Data Analysis and JMP L Phillips I Open the JMP program by going to Start Programs Statistics JMP 4 select II Open the data file students by clicking on the open data table button in the JMP starter window and scrolling over to the file students jmp The five columns contain the five variables Age an ordinal variable Sex a nominal or categorical variable Height a cardinal or numeric variable Weight a cardinal or numeric variable Idnum id number a nominal variable Note there are 233 observations or rows III To display ordinal and nominal variables from the menu bar choose analyze distributions In the distribution dialog box select the variables age and sex and drag to the y columns window Hit the OK button You can see there are more boys than girls and more twelve year olds than other ages The graph on the left for the variable age is a histogram plotting the frequency or number of observations for each age category The graph on its right is a mosaic bar chart showing the fraction of observations in each category By Oct 1 2002 Lecture 2 Econ240A 2 Exploratory Data Analysis and JMP L Phillips hitting the triangle button to the left of the word age and choosing histogram options you can add a count axis to the histogram IV To display a numerical variable click on the data window to make it active and from the menu bar choose analyze distributions In the distribution dialog box select the variables height and weight and drag to the y columns window Hit the OK button Use the hand icon and drag to the right to obtain finer categories of height You can see that the mode is 62 inches The maximum height is 72 inches and the minimum height is 51 inches The graph on the left for the variable height is a histogram plotting the frequency or number of observations for each height The graph on its right is an outlier box chart The ends of the box are the 25th and 75th quantiles quartiles 58 and 64 respectively The difference between these quartiles 6 is the inter quartile range a measure of dispersion Once again for height the 75th quartile is 64 with 25 of the observations lying above this height and the 25th quartile is 58 with 25 of the observations lying below this height so the inter quartile range is 6 The median height is 61 inches with 50 0f the observations above this height The median is illustrated in the box by a line The lines on either end of the box are whiskers and extend to the outermost data points within the distance for example 75th quartile 1 5 inter quartile Oct 1 2002 Lecture 2 Econ240A 3 Exploratory Data Analysis and JMP L Phillips range i e 64 1 5 6 or 73 Since the maximum height is 72 inches the whisker ends there Thus there are no outliers or heights to plot beyond this whisker The 25th quartile is 58 so the whisker will potentially extend down to 49 but the minimum height is 51 inches so the whisker ends at 51 and there are no outlier heights below this The diamond is the called the means diamond Note the mean or average height is 61 33 inches above the median of 61 The extent of the diamond is a 95 confidence interval around the mean i e the probabilty of the mean height lying above or below the diamond is only 5 We will study the calculation of these confidence intervals in the weeks ahead Note there is an outlier observation for the weight variable so this may be an individual that requires medical diagnosis The red bracket in the box plot designates the range of the shortest half of the data i e the 50 of the observations that are most dense i e clustered around the central tendency In the moments list are the mean and standard deviation of the observation values for example for height V The Spinning Plot Select the data window and from the graph menu choose spinning plot In the dialog box use the control key to select the height weight and age variables and drag to the y column box Click OK Oct 1 2002 Lecture 2 Econ240A 4 Exploratory Data Analysis and JMP L Phillips Note the positive relationship or correlation between weight and height as age increases Use the hand icon to rotate the three dimensional data plot Try using the white background You can use the lasso icon to select the outlier point and from the data table identify the idnum of this individual VI Help Menu The manuals are available online and provide instructions for using the JMP program Select help from the menu bar and select contents VII Analysis of a Subset of Female Students Use the students window and repeat the instructions at the beginning of section III above i e from the menu bar choose analyze distributions and select age and sex and drag to the y columns window Highlight females in the histogram Note that all of the observations for females are now selected in the data window From the Tables menu in the bar select subset In the dialog box choose a name such as female subset of students This data file can then be used to conduct analysis on the height weight and age variables as before including producing histograms and box plots as well as a rotating plot but restricted to females
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