Welcome to lecture 28. In this lecture, we will discuss about scatter diagram as one of the graphical methods to depict the relationship between two sets of data. scatter diagram developed by gf w PowerShell. In 1832. Dr. Ishikawa popularized this tool in Japan industries, he called it as one of the indispensable tools of quality control used to depict the relationship between two variables. relationship between two variables can be a strong correlation A weak correlation are no correlation at all.
Further the strong and weak correlations could either be positive correlation or a negative correlation. Let us see how these five types of correlation looks like. As you can see, in strong relation for every increase in one variable, there is a corresponding increase or decrease in other variable weak correlation. The data are not too clustered, as in strong correlations. Still, we could depict some pattern As you see the last graph, there is no correlation at all. Here is an example from one of the six sigma projects.
Here, the team was analyzing the correlation between soldier temperature and defect rates. for plotting scatter diagram, we need two variables identify the x and y variables identify the highest and lowest value of x and y respectively plot values of x and corresponding values of y on graph identify the time population. Let us try it with this data. Before we start, we need to identify the dependent data. here we can say that defect rate is dependent on solar temperature. Usually, we take y as the dependent variable and x as independent variable.
Then identify highest and lowest value from the datasheet from the data set plot x and y axis values based on the highest and lowest values now, plot Individual x and corresponding y from the data set. Finally, identify the pattern of correlation. By seeing this pattern, we can see there exist a strong negative correlation between solar temperature and defect rate defect rate decreases with the increase in solar temperature and vice versa. Let us try to do this exercise in Minitab. download the file and double click to open click graph. Then click scatter plot the scatter A plot dialog box will open.
Click simple and click OK. At this window, click on y variables and double click defect rate. Click on x variables and double click on soldier temperature. Click ok. scatterplot graphical window opens we can see where the pattern that there exists a strong negative correlation between these variables. That's all for this lecture about the scatter diagrams. Let us move to the third part of graph methods in the next lecture. Thank you.