Bivariate Descriptive Statistics: Unsing Spreadsheets to View and Summarize Data

Transcription

1 Connexions module: m Bivariate Descriptive Statistics: Unsing Spreadsheets to View and Summarize Data Irene Mary Duranczyk Suzanne Loch Janet Stottlemyer This work is produced by The Connexions Project and licensed under the Creative Commons Attribution License 3.0 Abstract Basic directions on how to use Google Spreadsheet and Excel to explore and summarize bivariate data. 1 Displaying Bivariate Data in Graphs In this section we will discuss techniques using a spreadsheet for displaying quantitative data using stemplots, histograms, boxplots and qualitative data using bar graphs and pie charts. We will primarily use Microsoft Excel and Google Spreadsheet, as we will use these two resources for sampling and surveying in this introductory course. 2 Categorical- Categorical We will review a few techniques that you will use to create, copy, and paste into a document, and save your displays of data. Contingency Tables: Excel - We will use pivot tables to create contingency tables. We have used them before for univariate data. This time we will highlight two columns of data to create our pivot tables. Both columns of data must be categorical. The two columns of data must be side-by-side. A good technique to use is to copy the two columns of data you want to display in a contingency table to a new labeled worksheet, side by side. The example below demonstrates that process. Version 1.1: Aug 21, :19 am

2 Connexions module: m Figure 1 I have two columns of data in a new worksheet labeled. When I mouse over the OK button, and click, the PivotTable Fields will appear and I can use them to create a contingency table. I usually select the variable with the least number of categories for the columns and the variable with the largest number of categories for the rows. This just makes the chart easier to cut and paste into a word document. In the example below I have dragged and dropped Where do you live? to the Columns eld and College Rank to the Rows eld. I can then either put college rank or where do you live in the Values eld. For this example I put college rank into the values eld. I now have a contingency table. See image below. I have only the counts in my contingency table. The next step will be to create row or column percents.

3 Connexions module: m Figure 2 I can now add another college rank to the Values eld to create a percent eld. I now have two college rank elds in my Values eld. I will create percentages for either row or columns by clicking on the down arrow next to the count of college rank and picking Value eld setting from the drop-down menu. When I pick value eld settings a pop-up menu will appear and you will select the tab that says Show Values As, and then from the drop-down menu of Show Values As, select percent of column or percent of rows. For this example I have picked percent of column since my data is mostly o campus. I can now see that 60 percent of the students from this sample that live o campus are seniors. I can use the percents to interpret my data. Note that when I created the second Values eld, a Value eld was created in the Columns eld. You don't create this eld, the Excel spreadsheet did that automatically from you creation in the Values eld. See image below. Also note that I highlighted my titles on the actual PivotTable and then from the home tab selected wrap text to make my columns neater. You can experiment with other editing of the titles to get the look you want.

4 Connexions module: m Figure 3 Google Spreadsheet You can create pivot tables in Google Spreadsheet as you did for univariate data however you have the same limitations, you cannot create row or column percentages unless you create them using formula (which you can do!) The only dierence here is that you will again highlight two columns of data that you want to look at in the pivot table and select one for the rows and one for the columns. See the image below. Go back to Sampling and Data to get more details on how to nd the Report Editor.

5 Connexions module: m Figure Bar Graphs (stacked and side by side): In both Excel and Google Spreadsheet, it is very easy to create side by side or stacked bar graphs directly from your contingency tables. Highlight the elds on your contingency table (note do not highlight the totals column or any of the cell highlighted blue) and then go to your insert tab and insert a chart. See the elds highlighted (the area highlighted grey with a green border around it) in the gure below. Figure 5

6 Connexions module: m You have a choice of side by side or stacked. In Excel you can use your percentages. In Google Spreadsheet you will need to create your percentages if you want them in your bar graphs. Below is output from Excel and Google Spreadsheet. Both spreadsheet programs give you many options in the design and format modes. In Excel you can access the design you want from the Change Chart Type eld on the Design Tab. In Google Spreadsheet you change chart types in the Chart editor under the start tab or the charts tab. Explore... it's fun. Figure 6

7 Connexions module: m Figure 7 Figure 8

8 Connexions module: m Pie Charts: Pie charts are created the same way as bar graphs in Excel and in Google Spreadsheets using the pivot table... however you will need to change the order of the columns to create multiple pie charts. If you use the sort function in the PivotTable eld (highlighted in green below) the eld at the top of the PivotChart Fields, mouse over the down arrow, a popup menu will appear, pick a dierent sort option (a to z, z to a, or more sort options), and then the order of your columns will change. See Image of the popup menu below. Figure 9 To make multiple pie charts you will need to copy the pie chart as a picture and paste it on your spreadsheet before you pick an alternative sort method. If you do not copy the pie chart as a picture, when you sort the data, you graph will change (it remains dynamic). Same is true when creating pie charts in Google Spreadsheet. 2.3 Optional Classroom Exercise for Categorical Categorical Data: At your computer, try this exercise: (1) Open the le, Statistics First Day of Class Survey that you worked on previously (2) open the le in Google Spreadsheet or Excel; (3) create a new worksheet tab and label it Bivariate Graphs for Categorical Data; (4) pick two column of data that are categorical and has been cleaned and create a contingency table, side by side bar graphs and side by side pie graphs with all the appropriate labels; And (5) save the le again and post in the appropriate Moodle assignment. 2.4 Categorical - Numerical When working with categorical and numerical data and Excel or Google Spreadsheet, one of the best rst steps is again, to copy the columns of data from your working data sheet to a new spreadsheet, and label the spreadsheet. The next step will be to sort the data. You must be sure to sort both columns of data together. The data from the categorical column and the numerical column are related. They are a pair

9 Connexions module: m of data from the same source. In examining categorical numerical data we want to know what is the relationship between the two responses, so we must keep the two columns together. Sorting Data: To sort data in Excel or Google Spreadsheet, you will go to the DATA tab and select sort data you want to sort by your categorical data based on the alphabet. Once you have sorted the data the order will change. Once you have the new order of your data you will need to copy in a separate column each of the numeric data for each unique categorical data source. See the example below. I have labeled each column by the category and have copied only the numeric data related to the category in the rows below the title of the column. Note that I used wrap text to keep my titles compact and I copied my data into the appropriate columns based on my titles. This is the same process in Excel and in Google Spreadsheet. Figure 10

10 Connexions module: m Figure 11 Descriptive Statistics: Once you have created your columns of sorted data you can select all of the columns and create your summary descriptive statistics using the Data Analysis Tool in Excel or by using formula to create you summary statistics in Excel or Google Spreadsheet.

11 Connexions module: m Figure 12

12 Connexions module: m Figure 13 Side by Side Histogram will need to be created individually as we did in Univariate Descriptive Statistics using the individual columns of data and then copy and pasting them side by side using either Excel or Google Spreadsheets. Side by Side Box Plots will also need to be create individually in Excel as we did in Univariate Descriptive Statistics however you will use the template especially created for multiple side by side box plots. Side by Side Stem and Leaf graphs also will use the same methods as we used in Univariate Descriptive Statistics. 2.5 Optional Classroom Exercise: At your computer, try this exercise: (1) Open the le, Statistics First Day of Class Survey that you worked on previously (2) open the le in Google Spreadsheet or Excel; (3) create a new worksheet tab and label it Bivariate Graphs for Categorical-Numeric Data; (4) pick two columns of data one that is categorical and one that is numerical and has been cleaned and sort your data by categories; (5) create your columns of

13 Connexions module: m sorted data with all the appropriate labels; (6) create your descriptive statistics for each of your categories of data; (7) create either side by side histograms, box plots, or stem and leaf graphs based on the descriptive statistics indication of shape, center, and spread; nally, (8) save the le again and post in the appropriate Moodle assignment. 2.6 Numerical Numerical When we have numerical-numerical data we can use the descriptive statistics that we had created previously, since we are not re-grouping the data. We will want to look at the relationship between the two numerical sets of data and to do that we will create a scatter plot, create a line of best t, create the equation for the line of best t and inspect the R and R 2 values. Scatterplots in Excel and Google Spreadsheet are very much the same. You will select your two column of data of interest, copy and paste them to a new spreadsheet and label the spreadsheet. Once that is complete you will highlight the two columns of data and go to the INSERT tab and insert scatter or bubble chart. The following popup window will appear after you click. Figure 14 You will now need to choose the graph and click OK to insert the graph into your page (in Excel) or Insert (in Google spreadsheet. You will then need to create labels for the axis. Once you click on OK or Insert this following screen will appear and if you mouse over and click on your scatterplot you will see the plus, paintbrush, and funnel appear to the right of the graph. Those tools will allow you to edit your scatterplot to make it look professional.

14 Connexions module: m Figure 15

15 Connexions module: m Figure 16 In Excel: Now choose the plus to edit your chart title, create your axis labels, and trendline. When you mouse over trendline a right facing arrow will appear. Click on that arrow and you will see a new pull down menu with the option to select, more options... Select that option and you will see another popup menu with the choice to select a Linear trendline, and then at the bottom of that trendline options list you will nd option boxes for Display Equation on chart, and Display R-squared value on chart. Put a check mark in both of these boxes and you are ready to describe the relationship between the two variables.

16 Connexions module: m Figure 17 In Google Spreadsheet: Click on the down arrow in the upper right hand corner and select advanced edit. You can there customize your chart adding a title and axis labels. You will not however be able to add the trendline or the equation easily. Excel is more advanced for this feature. You could also turn o legend since it is not necessary for this type of graph. It has a drop down menu with the option of none.

17 Connexions module: m Figure Optional Classroom Exercise: At your computer, try this exercise: (1) Open the le, Statistics First Day of Class Survey that you worked on previously (2) open the le in Google Spreadsheet or Excel; (3) create a new worksheet tab and label it Bivariate Graphs for Numeric-Numeric Data; (4) pick two columns of data (both numerical) and data has been cleaned; (5) create you're a scatterplot with all the appropriate labels; (6) create line of best t with R 2 ; (7) create a paragraph describing the relationship between the variables; nally, (8) copy and paste your scatterplot to a word document with your narrative description, save the le and post in the appropriate Moodle assignment.