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PSYC 3301

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Hold an election. What is the next best way to predict the outcome of the election? ... to predict the outcome of a presidential election, what population are ... – PowerPoint PPT presentation

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Title: PSYC 3301


1
PSYC 3301
  • Review of Statistics

2
Populations and Samples
Imagine 4 years from now Bush and Gore are again
running against each other. Someone asks you who
is going to win the election. What is the best
way to find out who will win the election?
Hold an election
What is the next best way to predict the outcome
of the election?
Take a poll
What is a poll?
3
Populations
  • A population is the group of interest as defined
    by the investigator.

If you are trying to predict the outcome of a
presidential election, what population are you
interested in?
The group of people who will vote on election day
What is the best way to find out about a
population?
Test, measure, or otherwise examine EVERYBODY in
the population
What is the next best way?
Take a sample
4
Samples
A sample is a subset of the population
Researchers are almost always interested in
populations, but as a practical matter you can
only study samples.
One of the most important functions of statistics
is to provide a set of tools that allow
researchers to make inferences about populations
when all they have is information about a sample.
5
Parameters and Statistics
A pollster determines that 51 of a sample of
1,500 potential voters will vote for Gore. Is
this an example of a parameter or a statistic?
statistic
A parameter is
a characteristic of a population
A statistic is
a characteristic of a sample
a Parameter is to a Population as a Statistic
is to a Sample
6
A quick note on sampling methods
Simple random sample Obtain a comprehensive list
of all the individuals in a population and
randomly select a subset from that list
This ensures that your sample is 1 unbiased
each individual in the population has an equal
chance of being chosen for the sample 2
independent selection of one individual does not
influence the selection of another
How does the typical political poll violate the
assumptions if random sampling?
7
Descriptive and Inferential Statistics
What are descriptive statistics?
Descriptive statistics produce numbers that
summarize or describes a sample
What are inferential statistics?
Inferential statistics allow you to use
measurements from a sample to estimate a
population parameter.
8
Estimating From a Sample
Imagine you have been contracted by Boeing to
design the seats for the new Boeing 797. How
could you determine how wide the seats should be?
Lets estimate REWs from the population of
potential airline passengers….
Randomly select samples of 5 from the data on the
next slide
9
(No Transcript)
10
Boeing Example
The mean of the population of numbers in the grid
is 17.040
What is the mean of your sample?
Is this a statistic or a parameter?
statistic
Is the mean of your sample exactly 17.040? Is the
mean of your sample exactly the same as the mean
of other samples in the class?
11
Relation between samples and populations
Because sample statistics are almost always
different from each other, and rarely equal to
population parameters, we use inferential
statistics to Estimate population parameters
from sample statistics
12
Variables Quantitative and Qualitative
A variable is measure that can change or vary
What are some examples of variables?
A quantitative variable tells you something about
the amount or degree of the variable
What are some examples of quantitative variables?
A qualitative categorizes items/individuals, but
does not provide information about magnitude.
What are some examples of qualitative variables?
13
S. S. Stevens Scales of Measurement
What is a nominal scale?
A scale that categorizes items
What is a ordinal scale?
A scale that categorizes and rank orders items
What is a interval scale?
A scale that categorizes and rank orders items,
and has equal intervals
What is a ratio scale?
A scale that categorizes and rank orders items,
has equal intervals, and a zero that means the
absence or none of the thing being measured
14
Scales of measurement examples
Give some examples of nominal scales?
Give some examples of ordinal scales?
Give some examples of interval scales?
Give some examples of ratio scales?
The classification of scales is important for
choosing the kind of statistic you will use.
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