Chapter 4
Statistics
Statistics are everywhere!
4.1
Population, Sample, and Data
Definition.
Statistics is the science of collecting, organizing, and summarizing data in such a way that valid
conclusions and meaningful predictions can be drawn from them.
•
Descriptive statistics – organizing and summarizing data
•
Inferential statistics – Estimation and decision making
4.1.1
Population versus Sample
Definition
(Population)
.
The set of entire collection of individuals or objects under study is called the popula
tion.
Collection of data from every member of the population,
•
allows a question about the population to be definitively answered;
•
may be expensive, time consuming, impractical, or sometimes impossible.
Definition
(Sample)
.
A sample is a subset (portion) of the population, selected for study in some prescribed
manner.
Using sample data rather than population data is
•
more practical than a census.
•
gives variable results with some possibility of a wrong conclusion being adopted.
A
good sample
is representative of the population from which it was taken.
Example 1:
There is a small company with 8 employees whose ages are 53 32 61 27 39 44 49 57. The
average age of these employees
54
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If we take a sample of three employees from this company and calculate the average age of those three
employees. Suppose the three values included in the sample are 32, 39, and 57. Then the mean age for this
sample is
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 Summer '08
 Staff
 Math, Statistics, Frequency distribution, Histogram, relative frequency

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