Histogram
last edited by: Daniel Krompholz on Sep 23, 2016 11:55 AM  login/register to edit this page  
A graphical representation of the distribution of numerical data. It is an estimate of the probability distribution of a continuous variable (quantitative variable). Histograms are used to describe the central tendency, dispersion, and shape of a statistical distribution. The histogram does not consider the influence of time on the variation that exists within a distribution. ApplicationsHistograms can be used to show how much variation exists in work, e.g., how much time it takes an organization to complete certain activities. As a picture of the data distribution that includes its spread and shape, a histogram provides clues about the variation that exists in the work performed. Distributions can be skewed in either a positive (tail of the distribution to the right) or negative (tail of the distribution to the left) direction from the center. By examining the spread and shape of a distribution, the extent of variation in a work process can be determined. This can provoke further discussions to identify the cause of variation and the measures needed to either control or reduce it. A histogram is a useful tool to display the data in order to identify current performance and show how work processes ar improving over time. ProceduresOnce you have collected a set of data for a repeated activity, complete the following steps.
InstructionsTo construct a histogram, the first step is to "bin" the range of valuesâ€”that is, divide the entire range of values into a series of intervalsâ€”and then count how many values fall into each interval. The bins are usually specified as consecutive, nonoverlapping intervals of a variable. The bins (intervals) must be adjacent, and are usually equal size. If the bins are of equal size, a rectangle is erected over the bin with height proportional to the frequency, the number of cases in each bin. In general, however, bins need not be of equal width; in that case, the erected rectangle has area proportional to the frequency of cases in the bin. The vertical axis is not frequency but density: the number of cases per unit of the variable on the horizontal axis. A histogram may also be normalized displaying relative frequencies. It then shows the proportion of cases that fall into each of several categories, with the sum of the heights equaling 1. As the adjacent bins leave no gaps, the rectangles of a histogram touch each other to indicate that the original variable is continuous. ExamplesAn example of a histogram, and the raw data it was constructed from, is shown below:


last edited by: Daniel Krompholz on Sep 23, 2016 11:55 AM  login/register to edit this page  
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