Page 221 - Applied statistics and probability for engineers

6

Descriptive Statistics

Statistics is the science of data. An important aspect of deal-
Chapter Outline ing with data is organizing and summarizing the data in ways
that facilitate its interpretation and subsequent analysis. This
6-1 Numerical Summaries of Data aspect of statistics is called descriptive statistics, and is the
subject of this chapter. For example, in Chapter 1 we pre-
6-2 Stem-and-Leaf Diagrams sented eight prototype units made on the pull-off force of

6-3 Frequency Distributions and prototype automobile engine connectors. The observations
Histograms (in pounds) were 12.6, 12.9, 13.4, 12.3, 13.6, 13.5, 12.6, and
13.1. There is obvious variability in the pull-off force values.
6-4 Box Plots How should we summarize the information in these data?
This is the general question that we consider. Data summary
6-5 Time Sequence Plots methods should highlight the important features of the data,
such as the middle or central tendency and the variability,
6-6 Scatter Diagrams because these characteristics are most often important for

6-7 Probability Plots engineering decision making. We will see that there are both
numerical methods for summarizing data and a number of
powerful graphical techniques. The graphical techniques are
particularly important. Any good statistical analysis of data
should always begin with plotting the data.

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