When is the best time to use a histogram?

Answer 1

When you are unsure what to do with a large set of measurements presented in a

table, you can use a Histogram to organize and display the data in a more user-

friendly format. A Histogram will make it easy to see where the majority of values

falls in a measurement scale, and how much variation there is. It is helpful to

construct a Histogram when you want to do the following (Viewgraph 2):

! Sum m arize large data sets graphically. When you look at Viewgraph 6,

you can see that a set of data presented in a table isn't easy to use. You can

make it much easier to understand by summarizing it on a tally sheet

(Viewgraph 7) and organizing it into a Histogram (Viewgraph 12).

! Com pare process results with specification lim its. If you add the

process specification limits to your Histogram, you can determine quickly

whether the current process was able to produce "good" products.

Specification limits may take the form of length, weight, density, quantity of

materials to be delivered, or whatever is important for the product of a given

process. Viewgraph 14 shows a Histogram on which the specification limits,

or "goalposts," have been superimposed. We'll look more closely at the

implications of specification limits when we discuss Histogram interpretation

later in this module.

! Com m unicate inform ation graphically. The team members can easily

see the values which occur most frequently. When you use a Histogram to

summarize large data sets, or to compare measurements to specification

limits, you are employing a powerful tool for communicating information.

! Use a tool to assist in decision m aking. As you will see as we move

along through this module, certain shapes, sizes, and the spread of data have

meanings that can help you in investigating problems and making decisions.

But always bear in mind that if the data you have in hand aren't recent, or you

don't know how the data were collected, it's a waste of time trying to chart

them. Measurements cannot be used for making decisions or predictions

when they were produced by a process that is different from the current one,

or were collected under unknown conditions.