Transcript Correlational resear..

Correlational Research
• Goal: Describe the relationship between two
variables in terms of:
– Direction
– Strength
• Pearson Correlation Coefficient
– -1  0  +1
Testing the significance of a correlation
– Is the correlation significantly different from zero?
• Null hypothesis: The correlation between
Social Support and Life Satisfaction is not
significantly different from zero.
• Alternative hypothesis: The correlation
between Social Support and Life Satisfaction is
significantly different from zero
• Conclusion: A significant correlation between
Social Support and Life Satisfaction was
observed, r (3) = .884, p < .05.
The Squared Correlation
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r
r2
0
0
.1
.01
.2
.04
.3
.09
.4
.16
.5
.25
.6
.36
.7
.49
.8
.64
.9
.81
1.0 1.0
The squared correlation provides
the proportion of overlap between
the two variables.
Correlation and Cause and Effect
• Requirements for a conclusion regarding cause
and effect:
– Time-Order relationship
• Cause  Effect
• Can’t know which variable occurred first.
– No other variable is responsible for the
relationship.
• The Third Variable Problem
Survey Methods
Types of questions
1. Open-ended
2. Close-ended
3. Partially open-ended (“Other” is added as an
alternative response)
4. Rating Scale
– Likert rating scale. To what degree does the
respondent agree with a statement.
Likert-type Item
• “How much do you agree with the following
statement?”
• “I plan to dedicate the rest of my life to
learning more about statistics.”
1-------------2------------3------------4------------5
Strongly
Disagree
Disagree
Neutral
Agree
Strongly
Agree
Reversed Likert-type Item
• “How much do you agree with the following
statement?”
• “My hatred for statistics extends to the very
core of my being.”
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Strongly
Disagree
Disagree
Neutral
Agree
Strongly
Agree
Types of items to avoid
• Loaded question
– Includes non-neutral or emotionally laden terms
– Ex. What is your opinion of the hideous new
statue?
• Leading question
– Attempts to influence the response
– Example. Shouldn’t first-year students be
allowed to bring a car to campus?
• Double barreled question
– Asks for more than one piece of information in a
single item.
Sampling Techniques
• Probability Sampling
– Random selection
– Stratified random sample
– Cluster sampling
• Non-Probability sampling
– Convenience sampling
– Quota sampling