Chapter 12

Statistical Process Control Charts

Back to List | Introduction | Historical Birth Rates | Employment of the Labor Force | Exercises

Introduction

The notion of statistical process control often leads one to think of manufacturing and assembly lines and defective items. However the various charts associated with process control can be applied to any situation where observations are being made at regular time intervals, watching for a particular event to occur. The examples in this project deviate from the industrial image of process control.

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Historical Birth Rates

The data found at http://lib.stat.cmu.edu/DASL/Datafiles/Birthrates.html, the Data and Story Library, is a candidate for process control analysis. The process here is giving birth, the oldest and truest of manufacturing industries.

The data contained here are collected for studying trends in childbearing among younger women. In particular, the data reflects the birth rates (per 10,000) among 23-year old women. A line of data such as: 132.2    1937

means that in 1937, the percentage of 23-year-old women giving birth was .

In preparation for the exercises, convert all the birth rates to percentages and construct a p-chart.

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Employment of the Labor Force

At the Bureau of Labor Statistics data site (http://www.bls.gov/data/') under Most Requested Series, find the data table for Total Nonfarm Employment for the years 1990 - 2000. This table contains the number of people from the current workforce employed in non-farming jobs.

Ignoring the year 2000 data, construct an chart for the years 1990-1999, and then proceed to the exercises for this project.

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Exercises

When you've completed each exercise, click "Submit for Grade" in order to submit your answers to your professor.

1.  

In the p-chart for the birth data, what is the value at the centerline? What are the upper and lower control limits?

2.  

Which picture most looks like the p-chart you constructed?

A.

B.

C.


3.  

In your chart for the employment data, what are the centerline, upper control limit and lower control limit values? Assuming that the size of the workforce remained approximately the same throughout the 90s, interpret and discuss your chart.

   


© 2000 by Addison Wesley Longman
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