A histogram is a bar graph which represents a frequency distribution—a graph that’s organised to show how often each possible outcome of a repeated event occurs. A manpower histogram can show how many people or hours will be needed to get a job done over time, so you can schedule the right number of workers for each stage of a project.
Manpower histograms are likely to be most useful in situations where the project is going to go through predictable stages: preparing and ramping up, a period of peak activity and a ramping down. Construction projects are a good example. Creating the histogram is a way of predicting the need for labour at each stage so you don’t have people waiting around for work or delays caused by being understaffed. On the other hand, in a factory that is producing a product on a continuing basis, the histogram would most often show a straight line, so it would not produce a lot of useful information.
To create the histogram, one axis, the horizontal line at the bottom of the graph, for example, can show the timeline for the project, and the vertical axis can plot the number of workers or the number of hours they are going to be working, so the bars' height shows how many people will be needed and where they stand on the timeline represents where they will be needed at that stage of the project. The typical distribution for this kind of project is an “S” curve, with a few workers at the start, sweeping up as the number of people and hours rises to the top, when most of the work is being done, and finally levelling off and declining when there is just a little left to be done.
You can use Excel or another spreadsheet program to produce a histogram. From the pull-down menus, select “Edit," "Fill" and "Series” to create the bins. For frequencies, choose “Tools," "Data," "Analysis" and "Histogram.” Alternatively, you can use a histogram creation program such as SBHisto Histogram Generator 1.2 (see Resources). This is a free basic program that can create histograms from plain text (ASCII) data files, without a lot of bells and whistles.