Overview of the Day

Research Methods

Statistical Reasoning

What Characterizes Science?

– The use of theory • conceptual schemes for:

– organizing scientific observations

– organizing facts

– generating hypotheses

– Empiricism: • confirming or falsifying theory

– with data and facts

– and using standard methods for collecting data

Why do we Need a Science ofPsychology

• Limits of common sense and casual reasoning– overconfidence – hindsight

• Perceptual limitations• Human nature is complex • Increase our understanding of why we behave

as we do and mechanisms underlying behavior

How do Scientists get Data?

• Scientific Method

– controlled procedures that help to rule out other explanations

Variables

• Causal mechanisms and outcomes– independent variable (assumed cause)– dependent variable (assumed effect caused by

independent variable)

• Example:– anxiety (IV) --> self-esteem (DV)

Types of Scientific Studies

• naturalistic observation

• correlational study

• field experiment

• laboratory experiment

Statistics

• What scientists use to:– summarize data– understand relationships between variables– estimate the probability of events occurring by

chance– make inferences

Sampling

• Population – everyone or thing in a particular class

• Sample – a portion of people or things in a particular

class

• Random sample– each person or thing has an equal probability of

being included in a sample

Summarizing Data

• Graphs and Histograms (bar graphs)

• Measures of Central Tendency

• Measures of Variability

• Measures of Association

Graphs

• Visual display of data grouped by categories – example: the percentage of 3rd graders whose

IQ scores fall within various intervals

Central Tendency

• Mean (the average)

• Median (score in the middle)

• Mode (most frequent score)

• Example: what is the mean, median, and mode of the following five heights: 60, 63, 63, 65, 67, 68, 69?

Variability

• Degree of dispersion around the middle– standard deviation

• Example 1: which sample would have the largest standard deviations in height?

– a classroom of CMU students

– all people in an elementary school

• Example 2: What would indicate the most consistency in free-throw performance (percentage made per game) in a season? a high or low standard deviation?

Degree of Association

• Correlation coefficient (-1.0, 0, +1.0)

• Degree to which two variables are associated with each other (does not imply causality)

• Examples: – height and weight– packs of cigarettes per day and incidents of

lung cancer

Summary

• Science and scientific method

• Variables and types of scientific studies

• Statistics

• Sampling

• Summarizing data (graphs, central tendency, variability, association)