Visually Measuring Variation
A special type of graph that allows you to “see” the
variation in your process. It is sometimes called a frequency
Each cell in a histogram is a chute that you are going to drop your
data points into. As points fall into the appropriate chutes, they
build on top of one another and a pattern begins to emerge.
up a histogram, subtract the lowest data point from the highest data
point and divide that number by 10 to determine the cell width. Be
sure to round the calculated number so that the cell widths are easy
A distribution that forms a bell-shaped curve is called a
Points that fall outside of the normal distribution
are called outliers and indicate something different than normal has
happened in the process. Outliers are important because they send up
an immediate red flag that something unusual happened in our
process. Whenever we get one of these strange situations, we must
immediately find out what caused it and eliminate the cause.