If double or multiple peaks occur, look for the possibilityĬoming from multiple sources, such as different suppliers or machine adjustments. Is a sharp demarcation at the zero point representing a bound. The majority of the data is just above zero, so there
Skewed distribution, and may also be bounded, such as the concentricity data in Figure F.17B.Ĭoncentricity has a natural lower bound at zero, since no If it appears skewed, you should understand the cause of this behavior. If the data isĪbout the center of the histogram, it is skewed. If your data is from a symmetrical distribution, such asīell-shaped normal distribution as shown in Figure F.17A, the data will be evenly distributed about the center of the data. We can also see if the data is bounded or if it has symmetry, such as is evidenced The variation is also clearly distinguishable: weīetween 75.003 and 75.007. In Figure F.16, the central tendency of the data is about 75.005.
Therefore, always use a control chartĭetermine statistical control before attempting to fit a distribution (or interpret the histogram).Īn excerpt from Six Sigma DeMYSTiFieD (2011 McGraw-Hill) by Paul KellerĪn advantage of the histogram is that the process location Out of control, then by definition a singleĭistribution cannot be fit to the data. If double or multiple peaks occur, look for the possibility that the data isĬoming from two different sources, such as two separate personnel groups, or two differently adjusted machines. The lower bound may be physically limited to zero. Some processes will naturally have a skewed distribution, and may also be bounded. Should understand the cause of the "skewness". If the data is not roughly evenly distributed about the center of the histogram, it is commonly called "skewed". If your data is from a symmetrical distribution, such as the Normal Distribution, the data will be evenly distributed about theĬenter of the data. Interpretation is the resulting shape of a distribution curve superimposed on the bars to cross most of