NonExperimental designs Correlational and Quasiexperiments Psych 231 Research

Non-Experimental designs: Correlational and Quasi-experiments Psych 231: Research Methods in Psychology

n Lab attendance is critical this week because group projects are being administered n Attendance will be taken. n Don’t forget Quiz 8 (chapters 9& 10) due Tonight Announcements

n Sometimes you just can’t perform a fully controlled experiment n n Because of the issue of interest Limited resources (not enough subjects, observations are too costly, etc). • Surveys • Correlational • Quasi-Experiments • Developmental designs • Small-N designs n This does NOT imply that they are bad designs n Just remember the advantages and disadvantages of each Non-Experimental designs

n Looking for a co-occurrence relationship between two (or more) variables n Example 1: Suppose that you notice that the more you study for an exam, the better your score typically is. n n This suggests that there is a relationship between study time and test performance. We call this relationship a correlation. n 3 properties: form, direction, strength Y 6 5 n 4 3 2 1 1 2 3 4 5 6 X Correlational designs For this example, we have a linear relationship, it is positive, and fairly strong

Linear Y Non-linear Y X Y Y X Form X X

Positive Negative Y • X & Y vary in the same direction Direction Y X • X & Y vary in opposite directions X

r = -1. 0 “perfect negative corr. ” -1. 0 r = 0. 0 “no relationship” r = 1. 0 “perfect positive corr. ” 0. 0 The farther from zero, the stronger the relationship Strength +1. 0

n Advantages: n Does not require manipulation of variable • Sometimes the variables of interest cannot be manipulated n n Allows for simple observations of variables in naturalistic settings (increasing external validity) Can look at a lot of variables at once Example 2: The Freshman 15 (CBS story) (Vidette story) • Is it true that the average freshman gains 15 pounds? • Recent research says ‘no’ – closer to 2. 5 – 3 lbs • Looked at lots of variables, sex, smoking, drinking, etc. • Also compared to similar aged, non college students For a nice review see Brown (2008) Correlational designs

n Disadvantages: n Do not make casual claims • Third variable problem • Temporal precedence • Coincidence (random co-occurence) • r=0. 52 correlation between the number of republicans in US senate and number of sunspots • From Fun with correlations n Correlational results are often misinterpreted Correlational designs Correlation is not causation blog posts: Internet’s favorite phrase Why we keep saying it

n Example 3: Suppose that you notice that kids who sit in the front of class typically get higher grades. n This suggests that there is a relationship between where you sit in class and grades. Daily Gazzett Children who sit in the back of the classroom receive lower grades than those who sit in the front. Possibly implied: “[All] Children who sit in the back of the classroom [always] receive lower grades than those [each and every child] who sit in the front. ” Incorrect interpretation: Sitting in the back of the classroom causes lower grades. Better way to say it: “Researchers X and Y found that children who sat in the back of the classroom were more likely to receive lower grades than those who sat in the front. ” Misunderstood Correlational designs Example from Owen Emlen (2006) Other examples: Psych you mind | Psy. Blog

n Sometimes you just can’t perform a fully controlled experiment n n Because of the issue of interest Limited resources (not enough subjects, observations are too costly, etc). • Surveys • Correlational • Quasi-Experiments • Developmental designs • Small-N designs n This does NOT imply that they are bad designs n Just remember the advantages and disadvantages of each Non-Experimental designs

What are they? n n n Almost “true” experiments, but with an inherent confounding variable General types • An event occurs that the experimenter doesn’t manipulate or have control over • • • Interested in subject variables • • Flashbulb memories for traumatic events Program already being implemented in some schools high vs. low IQ, males vs. females Time is used as a variable • age Relatively accessible article: Harris et al (2006). The use and interpretation of Quasi. Experimental studies in medical informatics Quasi-experiments

n Advantages n n n Allows applied research when experiments not possible Threats to internal validity can be assessed (sometimes) Disadvantages n n n Threats to internal validity may exist Designs are more complex than traditional experiments Statistical analysis can be difficult • Most statistical analyses assume randomness Quasi-experiments

n Nonequivalent control group designs n with pretest and posttest (most common) (think back to the second control lecture) Independent Non-Random Dependent Variable Assignment Measure Experimental group Dependent Variable Measure participants Measure Control group Measure – But remember that the results may be compromised because of the nonequivalent control group (review threats to internal validity) Quasi-experiments

Program evaluation n – Research on programs that is implemented to achieve some positive effect on a group of individuals. – – e. g. , does abstinence from sex program work in schools Steps in program evaluation – – – Needs assessment - is there a problem? Program theory assessment - does program address the needs? Process evaluation - does it reach the target population? Is it being run correctly? Outcome evaluation - are the intended outcomes being realized? Efficiency assessment- was it “worth” it? The the benefits worth the costs? Quasi-experiments

n Used to study changes in behavior that occur as a function of age changes n n Age typically serves as a quasi-independent variable Three major types n n n Cross-sectional Longitudinal Cohort-sequential Developmental designs

n Cross-sectional design n Groups are pre-defined on the basis of a preexisting variable • Study groups of individuals of different ages at the same time • Use age to assign participants to group • Age is subject variable treated as a between-subjects variable Age 4 Age 7 Age 11 Developmental designs

n Cross-sectional design n Advantages: • • Can gather data about different groups (i. e. , ages) at the same time Participants are not required to commit for an extended period of time Developmental designs

n Cross-sectional design n Disavantages: • Individuals are not followed over time • Cohort (or generation) effect: individuals of different ages may be inherently different due to factors in the environment • • • Are 5 year old different from 15 year olds just because of age, or can factors present in their environment contribute to the differences? • Imagine a 15 yr old saying “back when I was 5 I didn’t have a Wii, my own cell phone, or a netbook” Does not reveal development of any particular individuals Cannot infer causality due to lack of control Developmental designs

n Longitudinal design n Follow the same individual or group over time • Age is treated as a within-subjects variable • • Rather than comparing groups, the same individuals are compared to themselves at different times Changes in dependent variable likely to reflect changes due to aging process • Changes in performance are compared on an individual basis and overall time Age 11 Age 15 Age 20 Developmental designs

n Example n Wisconsin Longitudinal Study (WLS) • Began in 1957 and is still on-going (50 years) • 10, 317 men and women who graduated from Wisconsin high schools in 1957 • Originally studied plans for college after graduation • Now it can be used as a test of aging and maturation Longitudinal Designs

n Longitudinal design n Advantages: • Can see developmental changes clearly • Can measure differences within individuals • Avoid some cohort effects (participants are all from same generation, so changes are more likely to be due to aging) Developmental designs

n Longitudinal design n Disadvantages • Can be very time-consuming • Can have cross-generational effects: • Conclusions based on members of one generation may not apply to other generations • Numerous threats to internal validity: • Attrition/mortality • History • Practice effects • Improved performance over multiple tests may be due to practice taking the test • Cannot determine causality Developmental designs

n Cohort-sequential design n Measure groups of participants as they age • Example: measure a group of 5 year olds, then the same group 10 years later, as well as another group of 5 year olds n Age is both between and within subjects variable • Combines elements of cross-sectional and longitudinal designs • Addresses some of the concerns raised by other designs • For example, allows to evaluate the contribution of cohort effects Developmental designs

n Cohort-sequential design Cross-sectional component Time of measurement 1975 Cohort A 1970 s Cohort B 1980 s Cohort C 1990 s Age 5 1985 1995 Age 15 Age 25 Age 15 Age 5 Longitudinal component Developmental designs

n Cohort-sequential design n Advantages: • Get more information • Can track developmental changes to individuals • Can compare different ages at a single time • Can measure generation effect • Less time-consuming than longitudinal (maybe) n Disadvantages: • Still time-consuming • Need lots of groups of participants • Still cannot make causal claims Developmental designs

n What are they? n n Historically, these were the typical kind of design used until 1920’s when there was a shift to using larger sample sizes Even today, in some sub-areas, using small N designs is common place • (e. g. , psychophysics, clinical settings, expertise, etc. ) Small N designs

n n One or a few participants Data are typically not analyzed statistically; rather rely on visual interpretation of the data Observations begin in the absence of treatment (BASELINE) Then treatment is implemented and changes in frequency, magnitude, or intensity of behavior are recorded Small N designs

n Baseline experiments – the basic idea is to show: 1. when the IV occurs, you get the effect 2. when the IV doesn’t occur, you don’t get the effect (reversibility) § § Before introducing treatment (IV), baseline needs to be stable Measure level and trend Small N designs

n Level – how frequent (how intense) is behavior? n n Are all the data points high or low? Trend – does behavior seem to increase (or decrease) n Are data points “flat” or on a slope? Small N designs

n ABA design (baseline, treatment, baseline) – The reversibility is necessary, otherwise something else may have caused the effect other than the IV (e. g. , history, maturation, etc. ) ABA design

n Advantages n n n Focus on individual performance, not fooled by group averaging effects Focus is on big effects (small effects typically can’t be seen without using large groups) Avoid some ethical problems – e. g. , with nontreatments Allows to look at unusual (and rare) types of subjects (e. g. , case studies of amnesics, experts vs. novices) Often used to supplement large N studies, with more observations on fewer subjects Small N designs

n Disadvantages n n Effects may be small relative to variability of situation so NEED more observation Some effects are by definition between subjects • Treatment leads to a lasting change, so you don’t get reversals n Difficult to determine how generalizable the effects are Small N designs

n n Some researchers have argued that Small N designs are the best way to go. The goal of psychology is to describe behavior of an individual Looking at data collapsed over groups “looks” in the wrong place Need to look at the data at the level of the individual Small N designs