Math on Info: A James B. Bleeker Website: Statistics 101: Histogram Construction Using Minitab

Here we assume that the data have already been entered into the worksheet and some tasks have already been performed by Minitab, including the construction of a dot plot, as set forth in Dot Plot Construction Using Minitab Release 13. We begin with:

We flatten the Dotplot window to remove clutter. To do such, click the minimization button (third from right) in the upper right hand corner of the Dotplot window. We have:

Step 1. Click Graph on the top bar to obtain a drop down menu and move the cursor down to Histogram.... The cursor causes the selection to be highlighted.

Step 3. Move the cursor over the variable in the left most window of the dialog box and click it to obtain:

Note that the variable has been highlighted, and the letters of the Select button have become darkened and the button - activated.

Step 4. Move the cursor down to the Select button and click it. The variable name is entered into Line 1 of the Graph Variables: window.

In the first box of the Data display: window should be Bar and in the second box should be Graph. Here, there is nothing to change.

Step 5. Click the Edit Attributes... button to obtain the Bar dialog box:

Step 6. Click the arrowhead to the right of Fill Type to obtain a drop down menu.

Step 7. Click the second entry, "Solid," in the Fill Type menu list. This will permit us to select a fill color (as well as an edge color, type and width, if we wish a change) after the histogram is generated. We make no further selections in the Bar dialog box, as the color choices offered by the Bar dialog box are both miniscule (relative to those available after the histogram is generated) and uninteresting.

After clicking "Solid" in the menu list and the OK button in the Bar dialog box, we are back to the Histogram dialog box.

Although the "Footnote...," "Text...," and "Data Labels..." menu selections may be very useful under appropriate circumstances, for our histogram, only the "Title..." option is of interest.

The bottom half of the Title dialog box provides quite a number of options (including a very large selection fonts), although it does not provide the option of putting the title in bold print (one of the comparatively few options available in Excel). As we want the title to be horizontal and as the font size, font color, and title location is adjustable after the histogram is generated, we click the OK button in the Title dialog box to return to the Histogram dialog box.

By clicking "Grid...," one may summon the Grid dialog box, and then by entering X in the first box on line 1 and Y in the first box on line 2 and clicking the OK button, one may impose both vertical and horizontal lines in the graph area of the histogram. The horizontal lines may be useful for determining the frequency corresponding to a bar height, although the lines are sometimes off enough to make reading bar heights challenging. As (1) we will not impose a grid in this histogram, (2) any axis modifications that may be pertinent to our histogram may be done after the histogram is generated, and (3) the other Frame options need not concern us, we leave the Frame menu and move on to the next item.

Step 14. Click the arrowhead to the right of "Fill type:" to obtain a drop down menu.

Step 15. Click "Solid" in the drop down menu. This will permit us to select the color of the fill for the outer area of the histogram and the color, width, and type of outline for the histogram after the histogram is generated. (Recall that our color choices are much greater after generating the histogram.) We click the OK button in the Figure dialog box to bring us back to the Histogram dialog box.

Step 16. Click again the Regions arrowhead to obtain the Regions drop down menu.

Step 17. Click "Data..." in the drop down menu to obtain the Data dialog box for setting attributes of the graph area of the histogram.

Step 18. Click the arrowhead to the right of "Fill type:" to access a drop down menu and again click "Solid." This will permit us to select the color of the fill for the graph area of the histogram, as well as the color, width, and type of outline for the histogram's graph area, after the histogram is generated. (Recall that our color choices are much greater after generating the histogram.) We click the OK button in the Data dialog box to bring us back to the Histogram dialog box.

Step 19. Click the Options... button to obtain the Histogram Options dialog box.

This is where we select the type of histogram. On the web page Displaying Quantitative Data, we show the frequency, percent (relative frequency), and cumulative percent (cumulative relative frequency) histograms for our data set. Also, in this dialog box you specify whether the values on the x-axis should be given at the beginning and end of each bar interval or at the middle of each bar interval, by clicking the "CutPoint" radio button or the "MidPoint" radio button, respectively, below "Type of Intervals." (For examples of histograms with each set of axis values, see Displaying Quantitative Data.)

Leave the radio button next to "Frequency" on, we click the radio button next to "CutPoint," and click the radio button next to "Number of Intervals" and enter 7 in the box. We have:

Note: When you specify the number of intervals, the x-axis values may or may not fall at the ends of the intervals, i.e., the cut points. In this instance, it was known from prior construction that they would. To have ensured that the x-axis values fell at interval ends, the radio button next to "Midpoint/cutpoint positions" should have been clicked (in lieu of that next to "Number of intervals") and in the adjoining box should have been entered .44:1.28/.12 for (beginning value):(ending value)/(interval width). Suitable beginning and ending values may be selected by (1) ascertaining the smallest and largest data values, (2) determining a suitable incremental value, and (3) adjusting the smallest data value, the largest data value, or both in order to ensure that the (ending value) equals the (beginning value) plus some multiple of of the (interval width). Finally, if the intervals are numerous, Minitab's x-axis values will not coincide with cut points (or midpoints), save for happenstance or shrewd interval selection; rather, an x-axis with customary tick marks - such as 50, 100, 150, 200,... or 1000, 2000, 3000,... - will be chosen by Minitab.

Click the OK button of the Histogram Options dialog box to bring us back to Histogram dialog box for the final time.

Step 21. Double click the Histogram window to activate the Tools and Attributes bars.

Step 22. Drag the Tools and Attributes bars to the side and then click each bar of the histogram, the lower color icon in the Attributes bar, and the applicable palette color, to refill, in turn, each bar with the desired color.

Note that all of the colors above the horizontal line of the palette are the basic colors; those colors below the horizontal line are colors that have been added to the palette. To add colors to the palette, see Adding a Color to the Palette of Minitab Release 13.

Step 23. After completing such, click a vacant spot in the graph area of the histogram and again the lower color icon of the Attributes bar in order to make our selection of fill for the graph area.

Step 24. After clicking the applicable palette color for the graph area, click a vacant spot in the outer part of the Histogram window and again the lower color icon in the Attributes bar in order to make our selection of fill for the outer area.

Step 25. After clicking the applicable palette color for the outer area, double click the x-axis label for rewording:

After typing a new x-axis label in the window of the Text dialog box, clicking the OK button, and resizing and dragging the label some, we have:

Step 27. In the menu, click "Copy Graph" and then paste the histogram into a word document. This gives the below gif picture.

From Word, you may (if your intent is to place the picture on a web page) paste the picture into your web page editor and crop and resize it to preference. Resizing may significantly distort the image; cropping should present no problem.