In this 30th lecture, we are going to cover the most important graphical method of Six Sigma, the histogram. We have learned that the objective of Six Sigma is to reduce variation in any process. Common statistical tools for analyzing variation are control charts. This will be discussed in the control phase of this course. And the histogram as a graphical method to analyze variation. histogram is a frequency polygon in which data are grouped into classes.
Histogram is a tool to analyze variation, it is a descriptive statistic method to group data set into classes. Minimum preferred number of data is 40 for making histograms now, let us learn to construct histogram with the help of a set of data shown on screen are the weights of some product in grams. We are going to analyze the process variation in this data set. First step in constructing the histogram is to find the highest and lowest value From the dataset followed by finding the range, this is nothing but the highest value minus lowest value of the data set which is equal to 60 to minus 50. That is 12. Next step is to decide the number of cells based on the number of data points.
Normally accepted standard for a number of sales are as tabulated. Let's say, for less than 50 data, we can have nearly five sales. However, we have 90 data points in our set ends Let us select six cells. In Step three, calculate the approximate cell width. This is equal to range divided by number of cells, that is 12 divided by six is equals to two. In Step four, we round off the cell width, if required.
Now use the cell width to group the data and find out the number of data all the frequencies of data falling in that group. Here we have eight number of data points in range of 5252 grams. Similarly, 23 number of data points and the range of 52 to 54 grams and so on. Once we have completed all the above steps, we can move to draw the histogram add the y axis, plot the frequencies and the x axis, plot the cell width. Now, draw the bar graph according to frequencies corresponding to each cell with as depicted. Finally, the analysis part what can we conclude about the shape of histogram?
In one glance The shape of histogram is similar to the bell curve data are almost evenly distributed at either side of its central tendency. However, it is not always necessary to get a bowl shape with histogram. There are other interesting pattern or shapes that may arise while using histograms. Let us discuss some of the possible shapes of histogram a bell shaped pattern a symmetrical shape with a peak in the middle. This is a normal and natural distribution Double big pattern with two bill shaped distribution. It's just two distinct processes are at work right or left skewed pattern, a symmetrical shape and which peak is at either right or left of the distribution.
Drawing histogram is a tedious task. Let us learn how to create a histogram with the help of Minitab. Download and double click the histogram file. This file consists of two set of CTP data of some six sigma project namely internal leak. Travel. We will show you how to make a histogram of distant travel.
Practice yourself with other file. Click graph histogram histogram window opens. Click with fit and click OK. In the histogram with fit window, double click on this to travel and click OK. histogram window will open now, you can also see the mean and standard deviation of data set at the right hand side of the graph. Analyze histogram as we did in the earlier part of This lecture that's all was this lecture. This is an important lecture.
Histograms are extensively used in the Six Sigma projects. If you have understood, let us move further with next lecture on discrete probability distributions. Thank you