PSY 307 – Statistics for the Behavioral Sciences

1. PSY 307 – Statistics for the Behavioral Sciences Chapter 1

2. The Problem of Variability • How do we deal with the fact that people are different? • From each other • From themselves over time • How do we measure the behavior of groups instead of individuals? • How do we compare people in groups?

3. What is Statistics • A tool for discovering relationships and patterns in data. • A way of describing and comparing behavior of groups. • A way of presenting and supporting arguments empirically.

4. Two Kinds of Statistics • Descriptive statistics – tools for organizing and summarizing observations. • Tables, graphs, averages • Inferential statistics – tools for generalizing beyond the actual observations. • Hypothesis tests (t-test, ANOVA)

5. Two Kinds of Inferential Studies Survey – SOC/PSY 444 Random Sample Population (unknown scores) Sample (known scores) Experiment – PSY 433 Treatment Group (known scores) Random Assignment Volunteers (unknown scores) Compare Control Group (known scores)

6. Two Types of Data • The type of statistic used depends on whether data are numbers or words (or codes). • Quantitative – any single observation is an amount or a count. • Ranks – relative standing, order • Qualitative – any single observation is a class or category.

7. Numerical Codes • When data consists of classes or categories, sometimes numbers can be used to replace category names. • Male = 1, Female = 2 • Yes = 1, No = 2

8. What is a Variable • Variable – a characteristic or property that can take on different values. • Constant – an observation that has only one value. • Any single observation in a data set.

9. Types of Variables • Discrete – isolated numbers separated by gaps. • Most counts • Continuous – values have no restrictions. • Weight, reaction times • Rounded off continuous variables are approximate. • Rounding creates gaps.

10. Types of Variables Male/female Old/new Yes/No 1st, 2nd, 3rd Fresh, Soph Prvt, Cpl, Sergeant Age Temperature Response time Correct answers Examples Words can be coded using numbers Arrange in order then replace rank with number Continuous values become discrete when rounded off

11. Variables in Research • Independent variable – the variable manipulated by the investigator. • May be used to define groups. • Used to test hypotheses about causation. • Dependent variable – the variable measured, counted, or recorded by the investigator. • The outcome. • Confound – an uncontrolled variable that varies with the independent variable.

12. Two Kinds of Studies Experiment Independent Variable Active-Listening Training No Active-Listening Training Number of Communication Breakdowns Number of Communication Breakdowns Dependent Variable Is this a real or transitory difference? Observational Study Pre-existing Score for Active Listening First Variable Are the two variables related? Number of Communication Breakdowns Second Variable

13. Multiple Dependent Variables • Sometimes variables of interest cannot be manipulated (e.g., sex, poverty) but only measured. • Correlation studies -- studies with multiple dependent variables. • Goal is to identify relationships among the dependent variables measured. • Often used in observational research.