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Chapter 1: Introduction and Graphical Displays
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For example, if we were interested in studying the distribution of students on
a given campus who will vote in an upcoming national election, we may call
every twentieth student from a list of student names which are arranged in
alphabetic order. The sample will comprise of the group of students who
were actually contacted and responded to the call.
Next, we define what we mean by a census.
Definition: Census
A census is a sample of the entire population.
For example, a company may be interested in the distribution of the total
miles traveled by a fleet of their rental cars over a one-year period. The
company can collect total miles traveled for all their rental cars over the one-
year period. This set of data values will constitute a census of total miles
traveled by their fleet of cars.
Both populations and samples have characteristics that are associated with
them. These are called
parameters
and
statistics
, respectively. Parameters
are summary information for a population and statistics are summary
information for a sample.
Definition: Parameter
A parameter is a characteristic or a fact about a population.
For example, we may be interested in studying the distribution of the high
school grade point average (GPA) for students at a particular college. If the
high school grade point average GPA for all the students on the campus is
3.01 on a 4-point scale, then this will be the value of the population average
for the students or it will represent the value of a parameter. This is because
the population in this case constitutes all the students on the campus.