Reasoning in Psychology
Using Statistics
Psychology 138
2013
"There are three kinds of lies: lies, damned lies, and statistics.”
Mark Twain
“Statistics have a bad reputation. We suspect that statistics may be wrong, that people
who use statistics may be "lying" -- trying to manipulate us by using numbers to
somehow distort the truth. Yet, at the same time, we need statistics; we depend upon
them to summarize and clarify the nature of our complex society. This is particularly
true when we talk about social problems.”
Telling the Truth About Damned Lies and Statistics, Joel Best (2001)
• Scientific reasoning in psychology
– improve your ability conduct and consume psychological research
• Statistical Literacy
– the ability to follow and understand arguments from data
Course objectives
Reasoning in Psychology
Using Statistics
“It’s about almost everything in modern society.”
Bennett, Briggs, Triola (2003), Statistical Reasoning for Everyday life
• Statistics are tools, used to make decisions based
on data
– Descriptive statistics
– Inferential statistics
• Data are numbers with a context
– How were the numbers measured, what do they mean?
What are Statistics?
Reasoning in Psychology
Using Statistics
• Main points from the video
– Every statistical test starts with an
appropriate selection of subjects
– Inferences must be based on more
than one observation because of
variability
– Two types of error must be
controlled while testing hypotheses
– A decision is based on two things:
• The difference between groups
• The variability of the scores
Video review
Reasoning in Psychology
Using Statistics
•
Inferential statistics:
hypothesis testing –
rats, robots, and
roller skates
Wiley (1977)
• Scientific Method
Producing
Data
Describing
Data
Conclusions
from Data
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Ask the research question
Identify variables and formulate the hypothesis
Define your population
Select a research methodology
Collect your data from a sample
Analyze your data
Draw conclusions based on your data
Repeat
The research process
Reasoning in Psychology
Using Statistics
• Methodological basics: what are data and how they are produced
– Research methods
– Sampling
• Observation methods
• Experimental methods
• Quasi-experimental
– Variables
• Types
• Operational definitions
– Measurements
• Samples and populations
• Statistics and parameters
• Techniques
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Basic Probability
Experimental control
Reliability
Validity
• Continuous and discrete
• Scales of measurement
Producing Data
Reasoning in Psychology
Using Statistics
• Internal and external
• Confounds & Bias
• Descriptive Statistics: Statistical tools/procedures to help organize,
summarize, and simplify large sets of data (distributions)
– Describing a single distribution
• Tables and Graphs
• Properties
– Shape, Center, Spread
• Locating scores & Transforming distributions (z-scores)
– The Normal distribution (Unit Normal Table)
– Describing the relationship between 2 distributions
• Correlation (Pearson’s r)
Describing data
Reasoning in Psychology
Using Statistics
• Inferential Statistics: Procedures which allow us to make claims about
the population based on sample data
– Distribution of sample means – Hypothesis testing
• Central Limit Theorem
• Standard error
– Error types
• Type 1 (α)
• Type 2 (β)
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1-sample z test
1-sample t test
Related samples t-test
Independent samples t-test
Chi-squared test
Correlation and regression
– Estimation
• Point estimates
• Confidence intervals
Conclusions from Data
Reasoning in Psychology
Using Statistics