Experimental Psychology PSY 433 Chapter 2 Observation and Correlation

Does Country Music Cause Suicide? http://www.youtube.com/watch?v=-Xu71i89xvs Stack & Gundlach found that metro areas that played more country music had higher suicide rates, concluding that country music causes suicide. Maybe depressed people seek out sad music? http://www.jstor.org/stable/2580303 Or maybe it is a spurious correlation? http://www.tylervigen.com/spurious-correlations

Non-Experimental Research Variable -- a characteristic that can have different values (height, weight). Value -- usually a single, specific number (6 feet tall, 140 pounds). Measurement – the process of assigning numbers to entities in the world. In non-experimental research, variables may be measured, but nothing is being manipulated by the experimenter. No independent variable, just DVs.

Naturalistic Observation Methods for observing behavior in its natural environment. Behavior is complex and humans have limited attention span, so we delimit, or narrow, the range of behaviors we plan to observe. Reactivity -- subjects may behave differently than usual when they know they are being observed.

Unobtrusive Observation Unobtrusive observation -- subject is unaware of being observed in presence of observer Example: chivalry study, bathroom study. Unobtrusive measurement -- observer collects evidence in absence of subject and infers behavior of subject. Example: graffiti study, collecting scat There is a danger in anthropomorphizing or incorrectly interpreting what is observed. Participant observation – “going native”

Survey Techniques Gives a picture of people’s attitudes, beliefs, behaviors, and feelings about a topic. Sample from a population, then infer based on sample -- only as good as the sample. Return rate may produce sampling problem. Collect large amounts of data from large number of people quickly. Does not show causality among variables. Can also be used to provide data for the correlational method.

Relational Research Contingency Research Data is ex post facto Variables are presented in a contingency table. A Chi Square statistic is computed to determine whether relationships among variables exist. Values in the tables are “counts” or frequencies for categories, not measurements. Data is ex post facto

Correlational methods Correlation – a statistical technique that expresses the degree of linear relationship between 2 variables. If the correlation is high, a strong linear relationship exists. If the correlation is low, a weak relationship exists. If the correlation is zero, there is no relationship.

Correlation Coefficient (r) r is a numerical index of the degree of linear relationship between 2 variables. r is computed by taking into account pairs of scores – one score from one variable and the other score from another variable. Correlation coefficient (r) has a strength (0-1) and a direction (+ or -). r allows us to more precisely compare different sets of variables: SAT & GPA vs IQ & GPA

Using Coefficient (r) Does income level predict reading level? Measure income level at grade 1 Measure reading level at grade 1 Compute correlation between reading level & income: What if r = +1.0? What if r = -1.0? What if r = +.88? What if r = -.88? What if r = +.15? What if r = -.19? What if r = 0.0?

Values of r for Multiple Variables

Causality and Correlation The directionality problem -- for any correlation between X and Y: X may cause Y Y may cause X Z may cause both X and Y Classic examples: Hours watching violent TV & violent behaviors (+) Grades in physics & grades in statistics (+)

Spurious Correlations Spurious correlation -- a correlation exists but no causal relationship exists. Spurious correlations sometimes occur because both variables are mediated by a third variable. Classic examples: Number of churches in a town and number of murders. Number of toasters owned in a household and number of teen pregnancies. Kids in private schools get higher test scores.

Biases Selection bias – a kind of spurious correlation Students in Mississippi had a higher average SAT than in California even though California spent more per pupil than Mississippi. In Mississippi only top students took the SAT whereas in California nearly all took it. Restriction of range -- a correlation may underestimate the relationship between two variables if the range of either variable is restricted.

An Example of Restricted Range