A histogram is a bar graph that represents a frequency distribution -- organized to show how often each possible outcome of a repeated event occurs. A manpower histogram can show how many people or hours are 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, peak activity and ramping down. Construction projects are a good example. Creating the histogram is a way of predicting the need for labor at each stage so you don’t have people waiting around for work or delays caused by being understaffed. In a factory that is producing a product on a continuing basis, such a 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 time line for the project, and the vertical axis can plot the number of workers or the number of hours they are going to be working. The bars' height corresponds to the number of people needed and where they stand on the time line represents where they are 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 leveling off and declining when there is just a little is 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. This is a free basic program that can create histograms from plain text (ASCII) data files, without a lot of bells and whistles.