PSY 307 – Statistics for the
Behavioral Sciences
Chapter 1
What is Statistics
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A tool for discovering relationships
and patterns in data.
A way of describing and comparing
behavior of groups.
A way of presenting and supporting
arguments empirically.
Two Kinds of Statistics

Descriptive statistics – tools for
organizing and summarizing
observations.


Tables, graphs, averages
Inferential statistics – tools for
generalizing beyond the actual
observations.

Hypothesis tests (t-test, ANOVA)
Two Kinds of Inferential Studies
Survey – SOC/PSY 444
Population
(unknown scores)
Random
Sample
Experiment – PSY 433
Volunteers
(unknown scores)
Random
Assignment
Sample (known
scores)
Treatment Group
(known scores)
Compare
Control Group
(known scores)
Two Types of Data
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The type of statistic used depends
on whether data are numbers or
words (or codes).
Quantitative – any single
observation is an amount or a
count.

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Ranks – relative standing, order
Qualitative – any single observation
is a class or category.
Numerical Codes

When data consists of classes or
categories, sometimes numbers can
be used to replace category names.
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Male = 1, Female = 2
Yes = 1, No = 2
What is a Variable
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Variable – a characteristic or
property that can take on different
values.
Constant – an observation that has
only one value.

Any single observation in a data set.
Types of Variables

Discrete – isolated numbers
separated by gaps.

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Continuous – values have no
restrictions.

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Most counts
Weight, reaction times
Rounded off continuous variables
are approximate.

Rounding creates gaps.
Types of Variables
Examples
Nominal
Ordinal
Scale
Categories
Ranks
Interval/Ratio
Discrete
Discrete
Continuous
Words or codes
Numbers
Numbers
Male/female
Old/new
Yes/No
1st, 2nd, 3rd
Fresh, Soph
Prvt, Cpl,
Sergeant
Age
Temperature
Response time
Correct answers
Words can be
coded using
numbers
Arrange in
order then
replace rank
with number
Continuous values
become discrete
when rounded off
Variables in Research

Independent variable – the variable
manipulated by the investigator.

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Dependent variable – the variable
measured, counted, or recorded by the
investigator.


May be used to define groups.
Used to test hypotheses about causation.
The outcome.
Confound – an uncontrolled variable that
varies with the independent variable.
Two Kinds of Studies
Independent
Variable
Active-Listening
Training
No ActiveListening Training
Dependent
Variable
Number of
Communication
Breakdowns
Number of
Communication
Breakdowns
Experiment
Is this a real or transitory
difference?
First Variable
Second Variable
Observational Study
Pre-existing Score for
Active Listening
Number of
Communication
Breakdowns
Are the
two
variables
related?
Multiple Dependent Variables
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Sometimes variables of interest
cannot be manipulated (e.g., sex,
poverty) but only measured.
Correlation studies -- studies with
multiple dependent variables.
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Goal is to identify relationships among
the dependent variables measured.
Often used in observational research.