1. 1 G89.2228 Lect 1a Lecture 1a Perspectives on Statistics in Psychology Applications of statistical arguments Describing central tendency and variability

2. 2 G89.2228 Lect 1a Statistics in psychology Three perspectives –Mathematical statistical theory –Conventions, norms, heuristics –Flexible methodology for making empirical arguments

3. 3 G89.2228 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

4. 4 G89.2228 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

5. 5 G89.2228 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

6. 6 G89.2228 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?

7. 7 G89.2228 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.

8. 8 G89.2228 Lect 1a Example Question: Are women who have a miscarriage more depressed than women in general? If so, how much more depressed?

9. 9 G89.2228 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.