1G89.2228 Lect 1a
Lecture 1a
• Perspectives on Statistics in Psychology
• Applications of statistical arguments
• Describing central tendency and variability
2G89.2228 Lect 1a
Statistics in psychology
• Three perspectives– Mathematical statistical theory– Conventions, norms, heuristics– Flexible methodology for making
empirical arguments
3G89.2228 Lect 1a
Mathematical basis of statistics
• Formal definition of probability
• Formal sampling frames
• Explicit stochastic models
• Methods that follow deductively from assumptions
• Mathematical developments are based on theorems and proofs
4G89.2228 Lect 1a
Conventions, norms and heuristics
• Rules of evidence become statistical rules (e.g. “p<.05”)
• Rules developed and sold by persons studying mathematics
• Masses learn rules, not statistical theory
• Efficient, easy to communicate
• Rules can become rigid, arguments may not be examined critically
5G89.2228 Lect 1a
Statistics as "principled argument" (Abelson)
• Recognition that many (most) applications of mathematical statistics are approximate, not exact
• Weighing information provided by data and statistical analyses
• Comparison of alternate methods and assumptions
• Requires conceptual understanding of statistical reasoning, if not formal mathematical basis
6G89.2228 Lect 1a
Applications: Three papers from current literature
• What claims are made about psychological results?
• What statistical arguments support the claims?
• What must we know to evaluate these claims critically?
7G89.2228 Lect 1a
Most Common Question in Statistical Applications
• Inferences about populations from samples
• Central tendency: average (mean), median and mode
• Variability around mean
• Population or Sample?– We may compare two sets of three
persons because we are interested in them as individuals.
– We may also compare two sets of three persons because we are interested in the populations they come from.
8G89.2228 Lect 1a
Example
• Question: Are women who have a miscarriage more depressed than women in general? If so, how much more depressed?
9G89.2228 Lect 1a
Strategy:
• Identify women who have miscarriage and measure their level of depression using a standard scale.
• Examine distribution in sample– Calculate mean, median, mode. – Calculate variance, range.– Make plot of distribution.– Examine central tendency in light
of variation.