How to Make Graphs in EXCEL

Transcription

1 How to Make Graphs in EXCEL The following instructions are how you can make the graphs that you need to have in your project.the graphs in the project cannot be hand-written, but you do not have to use EXCEL to make them if you have another program that you prefer. These instructions are for the current version of Microsoft EXCEL. If you have a different version, the instructions will be very close but not necessarily the same. 1 Scatter Plots To make a scatter plot, first put the explanatory variable in the column A and then the response variable in column B, as in the table below. Note that the A and B the headings for the columns. You want to label the columns row 1, as I did, but you will want to use names that make sense in the context of the problem. So, if we had 5 pairs of data, the spreadsheet should look like: A B 1 Explanatory Response Hilight the entire region. Then, select the Chart tab. You will find the choices for graphs there. Select Scatter. There will be a few options, but you want the first one. Once you select this the graph will appear on the screen. The default title will be the heading for the response variable, so you will want to change this. To do that, double-click on the name of the chart and you can type the new title If you want to make the regression line appear in the graph, this can be done without even calculating the coefficients of the regression line (of course, you will have to find the regression line anyway as part of this project...). To add this trend line, right-click on any one of the data elements and a new menu will come up. One of the options there will be to add the trend line. If you right-click again, you will have options to format the trend line. Note: if you right-click on the plot but not on a data point, a formatting menu for the graph will come up and if you right-click on one of the grid lines, a third menu will come up that will allow you to format those and the axes. 1

2 We don t want to have to use the calculator to find the equation of the regression line, especially because of the quantity of data we are talking about, so fortunately, EXCEL can find that for us too. To find the slope, the command line is : =INDEX(LINEST(y range,x range),1) The y range is the values in the spreadsheet. In the example from above, you would express the y range as B2:B6. Similarly, the x range would be A2:A6. If we had 5 data pairs, the command line will look like : =INDEX(LINEST(B2:B6,A2:A6),1) To use this, type this line an empty cell of the graph. I would put a title in the cell to the left of it to indicate what it is. Similarly, we do essentially the same thing to find the y-intercept, except the formula we put in the cell would be : INDEX(LINEST(y range,x range),2) You can find the correlation coefficient in EXCEL as well. command. The syntax for this is : To do so, we use the CORREL =CORREL(y range,x range) In the case of the data above, the syntax would be : =CORREL(A2:A6,B2:B6) For example, if we included these commands in the spreadsheet sample above, it could look like : A B 1 Explanatory Response Slope Y -intercept Correlation coefficient Note that the values 3.6, 1.2 and are the values that the spreadsheet calculates. We would see the result but not the formula. You can do additional formatting by selecting the Layout tab, or in the Chart tab there will appear submenus when you create the plot and you can use those to format and edit as necessary. 2

3 2 Histograms There is a histogram tool in EXCEL that is part of the Analysis ToolPak. To see if you have this package and how to use it visit Without the package, we can make histograms even though there is no histogram option. First, put all of the data into one column. I will assume for the sake of this set of instructions that you have exactly 100 data elements. Next, we need to create an adjacent column of BIN boundaries which will define the histogram we want to build. For example, entering 10, 20,..., 100 down through C1:C10 will allow you to build a histogram with a range from 0 to 100 (with 10 total bins). These values you are inputing will be the upper endpoints of the classes. Note: the number of bins and the upper endpoints you need will vary depending on the quantity of data we have and the spread of that data. In cell D1, put in the formula =FREQUENCY(A1:A100,C1:C10) (where 100 should be replaced by the actual number of data entries you copied into Column A) and C10 should be replaced by the cell that contains the last BIN entry. Do not include headers in this formula! But don t press Enter yet - we want to complete the whole frequency table, so instead hold down Shift Control and then press Enter. If you are using a Mac, the command we need here is Command and Enter. To create the histogram, highlight the frequencies (the entries in column D) and select the Chart menu. Select Column and then use the first option, which is called Clustered Column. A bar graph will appear on the screen, Then, right-click on any of the columns and select Format Data Point. In the Options submenu,change the series overlap to 100% and change the Gap Width to zero. The resulting graph will be your histogram. Regardless of which chart you are making, you can edit the labels on the axes (and you need to - make the changes) by right-clicking and going into the options menu. 3

4 3 Box Plots First, we need to find the 5-number summaries for the different sets of data (males, females and combined). First, put the data for the entire population in column A, the data for the males in column B and the data for females in column C. I am going to suppose that there are exactly 100 data entries total, 50 of each gender. If you collect more data than this, the values you have will need to reflect this. Set up the 5-number summaries to look like the following (assuming the raw data is in columns A, B and C) : E F G H Total Males Females Minimum Q 1 Median Q 3 Maximum You should know the minimum and maximum of each set of data (you can click on the columns and sort them), so enter those in the appropriate cells. I will give the formulas now for finding the other values for the total set of data. To find the values for the other sets, use the exact same syntax, but put in the appropriate data range. To find the median, put the following command in appropriate: =MEDIAN(A1:A100) Again, be sure not to include the column headers in the range for the formulas. The commands to find the quartiles are almost the same. The only thing that is different between the two of then is a single digit - we use this digit to specify which quartile. The syntax for quartiles is : =QUARTILE(A1:A100,1) for the first quartile =QUARTILE(A1:A100,3) for the third quartile. The number at the end of the formula tells which quartile want. Now that we have all of the statistics we need, we now want to create the box plots. Highlight all of the 5-number summaries, including the labels and column headers. In the Chart menu, select Line Graph and choose the one called Marked Line. Then, press the Switch Plot button. We need do a little cosmetic work. First, right-click on each of the lines and select Format Data Series. Under Line, select No Line in the Color pull-down menu. Unfortunately, you do have to do each line individually. Now, right-click on a data point and in the menu, select Order. We need to change the order of the data to be Q 1, minimum, median, maximum, Q 3. Then, move to the Options menu and select High/Low Lines and Up/Down Bars. This creates a box around the first and last data 4

5 entry in each set and will put in the lines we want. This is why we needed to put the values in the spreadsheet in a different order than we are used to. If you want to change the markers so that they are lines instead of the random shapes, right-click on the marker and then select Format Data Series. You can change the marker shape in the Marker Style menu. 4 Median-Median Lines Looking at the two columns for the explanatory and response variables, we first want to sort the data by the explanatory variable. To do so, hilight both columns (not the headers) and right-click. Select Sort and then select Ascending to order the data. By hilighting both columns, it will keep the data paired. Next, we need to partition the data into the three sets. Remember, if the number of data elements is not divisible by 3, then we have to make the number of elements in each group symmetric. Once we partition the data, we can use the MEDIAN command 6 times, once for each of x and y for each set, and make a little table for this set of points. Next, we need the slope of the line. We can use the points and the the standard formulas here, but we will make EXCEL do the work. To find the median-median line, we could create a little table to the right of our data. E F G x median y median left middle right Here, the median of the left group is (F 2, G2), for the middle group is (F 3, G3) and for the right group is (F 4, G4). Now, to the right of this, I would create a new place to organize the lines. We need to find the equation of one line, the y-intercept of the parallel line and then the new y-intercept for the median-median line. The set of commands I would use are: slope of line containing left and right median points (in cell G6) = (G4 G2)/(F 4 F 2) y-int of line containing left and right median points (in cell G7) = G4 G6 F 4 y-intercept of parallel line passing through middle median point (in cell G8) = G3 G6 F 3 5

6 y-intercept of median-median line (in cell G9) = (2 G7 + G8)/3 As long as labeled the cells, you now have and know everything you need. To plot this line over the scatter plot, we need to use some trickery, since there is no way I know of to plot a line with parameters we input, and since the important part of this is finding the equation of the line, I do not think it is necessary to plot the line over the data set. 6