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© 2010 Radha Bose FSU Department of Statistics
Introduction
&
Sampling — 1
Read through this set of notes and attempt #16 on your own.
I will explain
#7 in class and then you will attempt #8 on your own.
Solutions to #18
have been posted on Blackboard.
PRELIMINARY DEFINITIONS
Subjects:
The objects from whom, or about whom, data is collected.
To identify the subjects in a story,
first identify the sample size
n
, then ask yourself "
n
of what are we getting information about?".
Observation:
A single collected data value (a piece of information), aka
data point
or
response
.
Each
subject will contribute exactly one observation to the raw data set.
To identify the observations, first
identify the subjects, then ask yourself "from each subject what piece of information are we getting?".
Sometimes the subjects and the observations are the same.
Population:
The entire group of subjects that we wish to get information about in a single study.
In
reality, it is often timeconsuming or costly to obtain data from the entire population under consideration,
so we usually work with samples.
Sample:
A subgroup of subjects within a population.
In real life, we would obtain data from a sample
instead of a population, and then use our knowledge of statistics to make inferences about the population
from which the sample was drawn.
Parameter:
A numerical measurement that describes a characteristic of a population.
Statistic:
A numerical measurement that describes a characteristic of a sample.
Very often sample
statistics are used as estimates for the corresponding population parameters.
The table below shows the symbols we use to represent some parameters and statistics that you
will encounter in this class.
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Introduction
&
Sampling — 2
Symbol
Name
Population Parameter
(generally Greek letters)
Sample Statistic (generally Latin
letters)
Size (number of subjects)
N
n
"
N
" often denotes total sample size
when more than one sample is involved
Mean (average)
μ
x
Variance
2
σ
2
s
Standard Deviation
s
Proportion (percent)
π
p
Correlation
ρ
r
1.
We want to know what percent of this term's Statistics students are also taking French.
We
randomly select 40 students in our class and ask if they are also taking French, answer YES or
NO.
It turns out that 15 of them say YES so we calculate that 37.5% of them are also taking
French.
FSU administrators want a truer percent so they poll all of this term's Statistics students
and find that 29.8% of them are also taking French.
Identify the following in the story.
Subjects:
Observations:
Population:
Sample:
Parameter:
Statistic:
2.
You want to know the average age of all the persons living in your household so you do the
calculation and the average turns out to be 16.4 years.
Your teacher wants to estimate the
average age of all the persons living in your household so she asks you your age, and you happen
to be 20 years old, so she says that her estimate is 20 years.
Identify the following in the story.
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This document was uploaded on 10/31/2011 for the course STAT STA2023 at FSU.
 Fall '11
 RADHABOSE

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