Reasoning in PsychologyUsing Statistics
Psychology 138
2013
Reasoning in Psychology Using
Statistics
Course objectives
• Scientific reasoning in psychology– improve your ability conduct and consume psychological research
• Statistical Literacy– the ability to follow and understand arguments from data
"There are three kinds of lies: lies, damned lies, and statistics.” Mark Twain
Telling the Truth About Damned Lies and Statistics, Joel Best (2001)
“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.”
Reasoning in Psychology Using
Statistics
What are 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?
Reasoning in Psychology Using
Statistics
Video review
• 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
• Inferential statistics: hypothesis testing – rats, robots, and roller skates
Wiley (1977)
Reasoning in Psychology Using
Statistics
The research process
• Scientific Method– 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
Producing Data
Describing DataConclusions from Data
Reasoning in Psychology Using
Statistics
Producing Data
– Research methods• Observation methods
• Experimental methods
• Quasi-experimental
– Variables• Types
• Operational definitions
– Measurements• Continuous and discrete
• Scales of measurement
– Sampling• Samples and populations
• Statistics and parameters
• Techniques
– Basic Probability
– Experimental control
– Reliability
– Validity• Internal and external
• Confounds & Bias
• Methodological basics: what are data and how they are produced
Reasoning in Psychology Using
Statistics
Describing data
• 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)
Reasoning in Psychology Using
Statistics
Conclusions from Data
– Distribution of sample means • Central Limit Theorem
• Standard error
– Error types• Type 1 (α)
• Type 2 (β)
– Hypothesis testing• 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
• Inferential Statistics: Procedures which allow us to make claims about the population based on sample data
