histogram

What is it?

A histogram is a bar graph of raw data that creates a picture of the data distribution. The bars represent the frequency of occurrence by classes of data. A histogram shows basic information about the data set, such as central location , width of spread , and shape. Use histograms to assess the system’s current situation and to study results of improvement actions. The histogram’s shape and statistical information help you decide how to improve the system. If the system is stable, you can make predictions about the future performance of the system. After improvement action has been carried out, continue collecting data and making histograms to see if the theory has worked.

Descriptive statistics, such as chi-square , kurtosis , and skewness  can help you interpret the histogram and can show you if the data distribution is normal.

Central location

Central location is the center of a set of data points. Mean, median, and mode are the statistics used to describe it.

Chi-square

A goodness-of-fit-test statistic used to test the assumption that the distribution of a set of data is similar to the expected distribution, such as a normal distribution.

Kurtosis

Kurtosis is a statistic that is used to measure the "flatness" or "peakedness" of a set a of data. It represents a measure of the combined weight of the tails relative to the rest of a distribution. As the tails of a distribution become heavier, the kurtosis will increase. As the tails become lighter, the kurtosis value will decrease.

Skewness

Skewness is a statistic that is used to measure the symmetry of the distribution for a set of data. A process that is skewed tails off to the left or to the right.