Foundations of Research 1 This is a PowerPoint Show Click slide show to start it. Click through it by pressing any key. Focus & think about each point; do not just passively click. To print: Click File then Print. Under print what click handouts (6 slides per page). This is a PowerPoint Show Click slide show to start it. Click through it by pressing any key. Focus & think about each point; do not just passively click. To print: Click File then Print. Under print what click handouts (6 slides per page). Dr. David J. McKirnan, 2015 The University of Illinois Chicago Do not use or reproduce without permission Complex Research Designs: Multiple Independent Variables. Foundations of Research 2 Psychology 242, Dr. McKirnan Complex Research Designs Foundations of Research 3 Topics: Testing hypotheses about > 1 independent variable Factorial Designs: Main effects, Additive Effects, Interactions Examples of complex experiments The interaction of drug use & attitudes on sex risk among gay men 3 Independent variables: alcohol and behavioral disinhibition The interaction of nature and nurture: Genetics & stress and depression 1/21/15 Complex Research Designs: Multiple Independent Variables. Foundations of Research 4 Psychology 242, Dr. McKirnan Multiple independent variables Testing hypotheses about > 1 independent variable Factorial Designs: Main effects, Additive Effects, Interactions Examples of complex experiments The interaction of drug use & attitudes on sex risk among gay men 3 Independent variables: alcohol and behavioral disinhibition The interaction of nature and nurture: Genetics & stress and depression Foundations of Research 5 The complexity of life Our world is far more complex than we can express in an experiment: Any effect, however strong, is influenced by the myriad of other variables that comprise the natural world; A research study addresses a model of the world: a simplified representation of how the world works; Simple experiments necessarily ignore many influences on the phenomenon we are trying to explain. As research becomes more complex, we are able to capture more diverse explanations. An an example, click the box to see the many variables that influence human obesity Foundations of Research 6 Main effects An experimental design with a Single Independent Variable [IV]. Manipulated by experimenter, to Test an a priori hypothesis, e.g.; Placebo v. active drug Intervention v. distraction group etc. Or: A Quasi-experiment representing a simple group contrast Both Predictor and Criterion (outcome) are measured, e.g.; Male v. female School 1 v. school 2, etc. Experimental groups [true experiments] Experimental groups [true experiments] Naturally occurring groups [quasi-experiments] Naturally occurring groups [quasi-experiments] The examples we have been using with the t-test tested a single Main effect: Foundations of Research 7 Psychology 242, Dr. McKirnan Multiple independent variables Do stressful life events lead to more depression? Number of major stressful events (Ages 21 to 26) Men were sorted into 5 groups, corresponding to # major life stressors they experienced from age 21 to 26. At age 26 men in groups 3 & 4 were significantly more likely to have lifetime major depression episode than groups 0 2 Partial data from Avshalom C., (2003), Science Magazine. E X A M P L E Example of a main effect Looking only at stress as an Independent Variable, there is a main effect of stress on depression. Foundations of Research 8 This tests a relatively simple theory: It links one hypothetical construct to one outcome Stress depression Arousal performance Gender sex-role attitudes Assumes the main effect is independent of other key variables. Of course in reality is it rare (impossible?) for an important outcome to be under the control of only one variable. Foundations of Research 9 Psychology 242, Dr. McKirnan Multiple independent variables Multiple variables in psychological research Link two or more hypothetical constructs to an outcome. Stress and genetic vulnerability depression Arousal and gender may affect performance Drugs and expectations sexual risk Test if an effect depends upon other key variable(s). One Independent Variable may affect the outcome only at one level of a second IV. Multiple Independent variables allow us to test more complex theories & hypotheses: Maltreatment affects depression (a main effect), but only for some groups (the interaction). Foundations of Research 10 Psychology 242, Dr. McKirnan Multiple independent variables Multiple variables in psychological research Link two or more hypothetical constructs to an outcome. Test if an effect depends upon other key variable(s). One Independent Variable may affect the outcome only at one level of a second IV. The first IV may have a different effect on the outcome at different levels of IV 2. Multiple Independent variables allow us to test more complex theories & hypotheses: Alcohol use leads to more emotional arousal (a main effect), but men get stimulated and women get sedated (the interaction). Foundations of Research 11 Psychology 242, Dr. McKirnan Multiple independent variables B. Testing hypotheses about 2 or more I.V.s 1. Separate, main effects of each I.V. ( Do each of these variables significantly affect the outcome?) 2. Additive effects of > 1 I.V.s simultaneously (What is the combined effect of these variables?) 3. Interaction of 2 or more I.V.s (Does the effect of one I.V. on the outcome depend upon a second variable...?) A. Including a control variable as an I.V. E.g., gender, age, race, etc. Test if the I.V. has the same effect within both groups Two uses of multiple Independent Variables Foundations of Research 12 Psychology 242, Dr. McKirnan 1. Block the data by gender, age, race, attitudes, etc. 2. Test if the main Independent Variable has the same effect within both groups. Stress leads to depression. Is this process the same for men and women? A. Including a control variable as an I.V. E X A M P L E Foundations of Research 13 ClickClick for a general, integrative overview of gender differences in depression. A. Including a control variable as an I.V. Shih, J.H, Eberhart et al. (2006) Differential Exposure and Reactivity to Interpersonal Stress Predict Sex Differences in Adolescent Depression. Jr. Clin. Child & Adol Psy, 35 (1), p Here.Here All adolescents tend to become depressed in response to either interpersonal or chronic stress. Girls respond much more strongly to specific episodes of interpersonal stress (e.g., argument with friend). Boys respond more strongly to chronic stress (not belonging). Adding gender to our analysis allows us to better understand stress among adolescents. E X A M P L E Foundations of Research 14 Psychology 242, Dr. McKirnan B. Testing hypotheses about 2 or more I.V.s E X A M P L E Examining both trauma and genetic vulnerability allows us to better understand the onset of depression. There is a general (main) effect whereby more trauma leads to greater likelihood of adult depression Foundations of Research 15 Psychology 242, Dr. McKirnan B. Testing hypotheses about 2 or more I.V.s E X A M P L E However the effect of trauma interacts with genetics Childhood trauma has no effect in people who have no genetic vulnerability. With increasing genetic vulnerability, increasing trauma increases the likelihood of depression This constitutes a more complex theory of depression depression results from the interaction of several variables. This constitutes a more complex theory of depression depression results from the interaction of several variables. Foundations of Research 16 Psychology 242, Dr. McKirnan Multiple independent variables Testing hypotheses about > 1 independent variable Factorial Designs: Main effects, Additive Effects, Interactions Examples of complex experiments The interaction of drug use & attitudes on sex risk among gay men 3 Independent variables: alcohol and behavioral disinhibition The interaction of nature and nurture: Genetics & stress and depression Foundations of Research 17 Psychology 242, Dr. McKirnan Multiple independent variables We use a Factorial Design to test hypotheses about 2 or more Independent Variables IV #1; Gender IV #2; Type of stressor DV: Depression Factorial Designs The first IVis crossed with the second IV. MaleFemale Interpersonal Chronic The Dependent Variable (Depression) is assessed for each combination of the IVs DV Foundations of Research 18 Psychology 242, Dr. McKirnan Multiple independent variables This allows us to test: The Main Effects of each IV; The Additive Effect of the two IVs together The Interaction of IV #1 by IV #2. IV #1; Gender IV #2; Type of stressor DV: Depression Factorial Designs MaleFemale Interpersonal Chronic DV Foundations of Research 19 Example: Factorial design testing 2 IVs Hypothesis : Coping skills delivered by a peer helps diabetics maintain blood sugar. Skills training None (Placebo / Distraction grp) High (experimental group) Trainer Nurse (Standard of care) Peer (experimental group) Independent Variables: Values: NB: This example & the data are completely made up Foundations of Research 20 Psychology 242, Dr. McKirnan Multiple independent variables The hypothesis rests on the interaction of two variables Adding a second IV of training condition tests a more complex theory of skills training. 4-group factorial Design Skills trainingDistraction Peer trainer Nurse Independent Variable 1 Experimental v. control groups IV #2 Training condition Dependent Variable: Glucose control (assessed for every combination of IV1 and IV2) DV = M glucose control Example: Factorial design testing 2 IVs Foundations of Research 21 Psychology 242, Dr. McKirnan Multiple independent variables No skills (Distraction) Skills Training Peer trainer Nurse trainer Independent variable 1 Independent variable 2 Each cell of the design represents both IVs: Each cell contains data for a specific combination of conditions peer, no skills M peer, skills M Nurse, no skills M Nurse, skills M Example: Factorial design testing 2 IVs Foundations of Research 22 Psychology 242, Dr. McKirnan Multiple independent variables Data Table No skills (Distraction) Skills TrainingRow Ms Peer trainer M peer, no skills M peer, skills Nurse trainer M nurse, no skills M nurse, skills Column Ms Independent variable 1Independent variable 2 4 data cells, each with a M value for the D.V. The Marginals show overall Ms for each I.V.: Skills v. no skills (a.k.a. main effect for skills) Peer v. nurse trainers (trainer main effect) Contrasts among individual cells show any interaction effects. no skills M skills M Peer trainer M Nurse trainer M Example: Factorial design testing 2 IVs This is a 2 x 2 factorial design: 2 independent variables Foundations of Research 23 Psychology 242, Dr. McKirnan Multiple independent variables Testing Main Effects (hypothetical data) No skills (Distraction) Skills Training Row Ms Peer Nurse Column Ms The amount of change is the same for both training groups. Here is a (completely made up) example of a main effect. Glucose control is enhanced by skills training Foundations of Research 24 Psychology 242, Dr. McKirnan Multiple independent variables Alternate display of two Main Effects (hypothetical data) An alternate display of the same main effect data Skills training helps, by about the same amount no matter who it is delivered by. These data would support a simple Main Effect of skills training Foundations of Research 25 Data set 2.No skills (Distraction) Skills training Row Ms Peer Nurse Column Ms Two (additive) Main Effects The data show a main effect of trainer (Peers do better than nurses). And of skills training: Getting skills training helps about the same in both groups but contact with a peer is generally more helpful Here is an example of an Additive Effect. Training generally helps Foundations of Research 26 Psychology 242, Dr. McKirnan Multiple independent variables Additive Main Effects (hypothetical data) Adding these effects together shows a very high value for patients who get skills training by a peer Foundations of Research 27 Psychology 242, Dr. McKirnan Multiple independent variables Additive main effects: alternate display Here is an alternate display of the additive effect. General effect of trainer: peers do better than nurses no matter what the intervention and, getting skills helps, whether they are delivered by a nurse or a peer Foundations of Research 28 Psychology 242, Dr. McKirnan Multiple independent variables Alternate display of two additive main effects Alternate display of additive effect of two variables These two effects add up: Skills delivered by a Peer have the best results. Foundations of Research 29 Psychology 242, Dr. McKirnan Multiple independent variables Interaction Effects (hypothetical data) Data set 3.No skills (Distraction) Skills training Row Ms Peer trainer Nurse trainer Column Ms But only among patients trained by a peer. Skills training made a difference For patients trained by a Nurse, training had little effect Here is an example of an Interaction Effect of trainer by training condition. Foundations of Research 30 Multiple independent variables Interaction Effects (hypothetical data) Data set 3.No skills (Distraction) Skills training Row MsPeer trainer Nurse trainer Column Ms Since these data show an interaction, our graph shows the 4 individual cell Ms. The group that improved was the specific combination of: Skills Delivered by a peer Here is an example of an Interaction Effect of trainer by training condition Foundations of Research 31 Psychology 242, Dr. McKirnan Multiple independent variables Alternate Display of interaction effect (hypothetical data) Here is an alternate display of an interaction between two variables There is a large overall effect of training versus distraction, Interaction: the effect of the 1 st Independent Variable (training) depends upon the 2 nd IV (peer v. nurse). Overall M for skills training Overall M for distraction (placebo) not the nurse. but only for the peer trainer, Foundations of Research 32 Click 1 Psychology 242, Dr. McKirnan Multiple independent variables What is a main effect ? a. The simple effect of one I.V. on the D.V. b. One IV combines with another IV to produce an effect on the DV. c. One IV has an effect on the DV only at one level of another IV. d. An IV has a different effect on the DV at different levels of a second IV. Foundations of Research 33 Click 2 Psychology 242, Dr. McKirnan Multiple independent variables What is an additive effect ? a. The simple effect of one I.V. on the D.V. b. One IV combines with another IV to produce an effect on the DV. c. One IV has an effect on the DV only at one level of another IV. d. An IV has a different effect on the DV at different levels of a second IV. Foundations of Research 34 Click 3 Psychology 242, Dr. McKirnan Multiple independent variables What is an interaction ? a. The simple effect of one I.V. on the D.V. b. One IV combines with another IV to produce an effect on the DV. c. One IV has an effect on the DV only at one level of another IV. d. An IV has a different effect on the DV at different levels of a second IV. Foundations of Research 35 Psychology 242, Dr. McKirnan Multiple independent variables Testing hypotheses about > 1 independent variable Factorial Designs: Main effects, Additive Effects, Interactions Examples of complex experiments The interaction of drug use & attitudes on sex risk among gay men 3 Independent variables: alcohol and behavioral disinhibition The interaction of nature and nurture: Genetics & stress and depression Foundations of Research 36 Psychology 242, Dr. McKirnan Multiple independent variables Example of interaction effect; AIM study Following is an example of a statistical interaction from baseline (or pre-test) interviews conducted as part of a behavioral intervention trial. The two independent variables were measured only, making this a quasi-experiment. These findings illustrate the first type of interaction: The effect of the first Independent Variable on the outcome only occurs at one level of the 2 nd IV. The second type of interaction the effect of IV #1 is actually different depending upon IV #2 will be illustrated in the next example. Foundations of Research 37 Psychology 242, Dr. McKirnan Multiple independent variables Example of interaction effect; AIM study People who use drugs during sex are more likely to have unsafe (as well as more) sex. What causes that The drugs themselves (disinhibition) Some characteristics of people who use them? These are data from the Awareness Intervention for Men study of interventions for unsafe sex among MSM who use drugs. Sexual Risk among gay & bisexual men who combine alcohol and drugs with sex. Foundations of Research 38 Psychology 242, Dr. McKirnan Multiple independent variables Example of interaction effect; AIM study, 2 Two main effect hypotheses: McKirnan, D.J, Vanable, P., Ostrow, D., & Hope, B. (2001). Expectancies of sexual escape and sexual risk among drug and alcohol-Involved gay and bisexual men. Journal of Substance Abuse, 13, Paper here.here Implications for theory: Interventions should focus on attitudes & motivations as well as simple drug use. A simple bio-behavioral hypothesis would be that drug use per se. has brain-based disinhibiting effects, which can lead to sexual (and other) risks. Cognitive escape theories hypothesize that using drugs to avoid having to think about personal problems or risks can lead to both more drugs and drugs + risk. Drug use: Attitudes: Interaction hypothesis: Drugs make people more risky, but primarily if they also have high risk (escape) attitudes. Foundations of Research 39 Psychology 242, Dr. McKirnan Multiple independent variables Example of interaction effect; AIM study, 3 Sexual Risk Two Main effects: Independent of drug use, men with higher cognitive escape motives reported more risk. Independent of motives, higher drug use led to more risk. Foundations of Research 40 DV: risk levels Low drug use High drug use Low escape motive High escape motive With the factorial design, we summarize all 4 means in our table. The effect of Cognitive Escape motivation Foundations of Research 41 DV: risk levels Low drug use High drug use Low escape motive High escape motive With the factorial design, we summarize all 4 means in our table. And the effect of Drug Use. Foundations of Research 42 DV: risk levels Low drug use High drug use Low escape motive High escape motive With the factorial design, we summarize all 4 means in our table. Filling in the cells of the design shows us the interaction effect. As we can see, the Highest risk is among men with both high drug use and strong cognitive escape motives. Foundations of Research 43 Psychology 242, Dr. McKirnan Multiple independent variables Sexual Risk Overall / Interaction finding: Drug users with strong escape attitudes were very risky. Drug users without escape attitudes were less risky. For men who did not use drugs, attitudes did not affect risk. Drugs & attitudes interact: Drugs lead to risk primarily in the escape group. Drugs & attitudes interact: Drugs lead to risk primarily in the escape group. Foundations of Research 44 Alternate display of interaction effect Psychology 242, Dr. McKirnan Multiple independent variables No drug use: risk stays low for all participants Drug users: risk is high, but primarily among those with strong expectancies Foundations of Research 45 Psychology 242, Dr. McKirnan Multiple independent variables Testing hypotheses about > 1 independent variable Factorial Designs: Main effects, Additive Effects, Interactions Examples of complex experiments The interaction of drug use & attitudes on sex risk among gay men 3 Independent variables: alcohol and behavioral disinhibition The interaction of nature and nurture: Genetics & stress and depression Fillmore, M. T., & Weafer, J. (2004). Alcohol impairment of behavior in men and women. Addiction, 99 (10), Article here.here Foundations of Research 46 Psychology 242, Dr. McKirnan Multiple independent variables Example: 3 independent variables Core Hypotheses: 1.Men get more aroused by alcohol, women get less aroused. 2.Men are less able to inhibit behavior in response to alcohol than are women. Theories : Social learning: Men are socialized to lessen behavioral control in alcohol-related situations, women socialized to increase caution. Bio-behavioral: Basic inhibitory mechanisms in men are more reactive to alcohol and other drugs than in women Operational Definition of Behavioral Inhibition: Participants are given a go prime + a dont press stimulus Can they inhibit pressing the button? Operational Definition of Arousal: Two standard questionnaires: subjective stimulation & sedation. Foundations of Research 47 Experimental Design Psychology 242, Dr. McKirnan Multiple independent variables There are two Dependent Variables (or parallel studies) : 1.Emotional arousal after consuming alcohol (or a placebo). 2.Disinhibition; loss of the ability to inhibit a response after being primed to do so. There are four Independent Variables. Both studies provide alcohol v. placebo beverages (IV #1) to men v. women (IV #2). Study 1: Assessment of arousal v. stimulation (IV #3). Study 2: Go prime v. No-Go prime (IV #4). Provide 2 questionnaires: Subjective arousal / stimulation Subjective sedation (First Dependent variable represents a repeated measure ) Conduct a simple reaction time task Participants told to: a.press a button quickly in response to a go stimulus, b.do not press with a no go stimulus. (Second Dependent variable) Participants are first a. primed to expect a go stimulus (go prime) b. primed to expect a no-go stimulus. (3 rd Independent variable also a repeated measure) Foundations of Research 48 Psychology 242, Dr. McKirnan Multiple independent variables Subjective sense of stimulation Subjective sense of sedation Questionnaires Alcohol: Yes No Gender: Male Female Participant variables First 2 Independent Variables 1 measured, 1 manipulated Third Independent Variable Repeated measure: Stimulation v. sedation Design: 1 st Dependent Variable: Arousal Level Foundations of Research 49 Cues & stimuli: alcohol disinhibition Psychology 242, Dr. McKirnan Multiple independent variables Told there is a 80% likelihood of a No- Go stimulus Told 80% like- lihood of a Go stimulus PrimeStimulus Go No- Go Behavioral inhibition condition; Can you not press when expecting go, but suddenly told no-go. Behavioral inhibition condition; Can you not press when expecting go, but suddenly told no-go. Foundations of Research 50 Psychology 242, Dr. McKirnan Multiple independent variables no-go Actual target stimulus no-go go Expect go stimulus Expect no-go stimulus Participant priming yes Dependent Variable: Button press? yes no Alcohol: Yes No Gender: Male Female Participant variables First 2 I.V.s Third I.V. Repeated measure: each person gets both conditions Common procedure Assess no-go condition only Pressing in the no-go condition = disinhibition Design: 2 nd DV: Impulse Control Foundations of Research 51 Psychology 242, Dr. McKirnan Multiple independent variables MaleFemale Alcohol Stimulation questionnaire Sedation questionnaire Stimulation questionnaire Sedation questionnaire No alcohol Stimulation questionnaire Sedation questionnaire Stimulation questionnaire Sedation questionnaire (repeated measure) IVs: Gender Alcohol Consumption Type of arousal participants are men, women get alcohol, get placebo of participants in each cell Each participant gets both questionnaires 2 x 2 x 2 = 8 cells, using 4 sets of participants. Fullfactorial designwith arepeated measure: Design: 1 st Dependent Variable: Arousal Level Foundations of Research 52 Psychology 242, Dr. McKirnan Multiple independent variables MaleFemale Alcohol go primeno-go primego primeno-go prime No alcohol go primeno-go primego primeno-go prime (repeated measure) IVs: Gender Alcohol Consumption Priming condition participants are men, women get alcohol, get placebo of participants in each major cell Each participant gets two conditions 2 x 2 x 2 = 8 cells, using 4 sets of participants. Fullfactorial designwith arepeated measure: Design: 2 nd DV: Impulse Control (repeated measure) Foundations of Research 53 First Dependent Variable Psychology 242, Dr. McKirnan Multiple independent variables Hypotheses : 1.Alcohol leads to significant mood changes v. a placebo beverage a.stimulation & arousal b.Sedation 2.Mood changes vary according to participant gender a.Men stimulation b.Women sedation Statistical test: 3-way interaction Alcohol v. Placebo Alcohol v. Placebo Male v. Female Male v. Female Stimulation v. Sedation Stimulation v. Sedation XX Foundations of Research 54 Psychology 242, Dr. McKirnan Multiple independent variables Figure 3 Mean ratings of subjective stimulation on the BAES under 0.65 g/kg alcohol and placebo in women and men. 1 st DV: 2-way interaction for stimulation Alcohol led to more stimulation than did the placebo But primarily among men rather than women There was a 2-way interaction of gender (male v. female) by alcohol level (alcohol v. placebo) on stimulation. Alcohol use (IV # 1) led to stimulation, but only at the male level of IV #2 (gender). Foundations of Research 55 Psychology 242, Dr. McKirnan Multiple independent variables Figure 3 Mean ratings of subjective sedation on the BAES under 0.65 g/kg alcohol and placebo in women and men. 1 st DV: 2-way interaction for sedation Alcohol led to more sedation than did the placebo But primarily among women rather than men There was also a 2-way interaction of gender (male v. female) by alcohol level (alcohol v. placebo) on sedation. Alcohol use (IV # 1) led to sedation, only at the female level of IV #2 (gender). Foundations of Research 56 Psychology 242, Dr. McKirnan Multiple independent variables 1 st DV: show contrast condition Alcohol (v. placebo) made men more stimulated. Alcohol made women more sedated Figure 3 Mean ratings of subjective stimulation and sedation on the BAES under 0.65 g/kg alcohol and placebo in women and men. There was a 3-way interaction of gender (male v. female) by alcohol level (alcohol v. placebo) by arousal (stimulation v. sedation). Foundations of Research 57 Psychology 242, Dr. McKirnan Multiple independent variables M BAES subscale scores Alternate portrayal of 3-way mood interaction Placebo conditions do not show much effect The alcohol conditions show a classic cross-over effect for gender & mood; Men get aroused Women get sedated Foundations of Research 58 External validity: 3-way interaction Psychology 242, Dr. McKirnan Multiple independent variables How much external validity does this finding have? Foundations of Research 59 Psychology 242, Dr. McKirnan Multiple independent variables Alcohol & gender results 1 Figure 1 Mean proportion of failures to inhibit responses to no-go targets following go and no-go cues under 0.65 g/kg alcohol and placebo in women and men. Dependent variable 2: disinhibition of button press Alcohol disinhbition is much stronger for men than for women But only with a go prime. not for the no-go prime. Foundations of Research 60 Psychology 242, Dr. McKirnan Multiple independent variables Summary of the 3-way interaction 1.Alcohol (vs. no alcohol) makes it difficult to inhibit behavior 3.when they are primed to act, (vs. when they are primed to keep from acting). 2.primarily among men (v. women) How much external validity does this finding have? Foundations of Research 61 Multiple independent variables Testing hypotheses about > 1 independent variable Factorial Designs: Main effects, Additive Effects, Interactions Examples of complex experiments The interaction of drug use & attitudes on sex risk among gay men 3 Independent variables: alcohol and behavioral disinhibition The interaction of nature and nurture: Genetics & stress and depression Foundations of Research 62 Psychology 242, Dr. McKirnan Interaction of genetics & stress on depression. Overall hypothesis: Consistent with epigenetics perspective, stress may switch on genes that confer vulnerability to depression Independent variables: Variations in a gene that controls serotonin production in the brain [a measured variable]. The number of serious stressful life events between ages 21 and 26 [also a measured variable] Outcome variables: Symptom counts Major depression episode Suicide attempt Others reports of depression Avshalom C., et al. (2003). Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene. SCIENCE, 301 (July 18), [www.sciencemag.org]. [See readings: summary or the actual article.]summary actual article Foundations of Research 63 Psychology 242, Dr. McKirnan Interaction of genetics & stress on depression. 3 levels of genetic disposition. 5 levels of stress. 4 outcome measures (DVs). Foundations of Research 64 Psychology 242, Dr. McKirnan Multiple independent variables Interaction of genetics & stress on depression. More stress = more depression on all measures Foundations of Research 65 Psychology 242, Dr. McKirnan Multiple independent variables Interaction of genetics & stress on depression. But primarily among genetically vulnerable people Foundations of Research 66 Key genotypes and stress Psychology 242, Dr. McKirnan Multiple independent variables High vulnerability Low vulnerability Stress leads to depression only for those who are genetically vulnerable. This is illustrated by different stress depression effects for two key genotypes. Foundations of Research 67 Psychology 242, Dr. McKirnan Multiple independent variables Interaction of genetics & stress on depression; Trauma. Interaction is very strong in an analysis of childhood trauma and depression. People with no genetic vulnerability: childhood trauma has no effect on depression People with increasing genetic vulnerability: More trauma greater likelihood of depression. Foundations of Research 68 Psychology 242, Dr. McKirnan Multiple independent variables Multiple IVs; summary 1 Main effect: Test how one IV in isolation affects the DV Multiple Independent Variables / Predictors tell us much more than simple main effects. # of major stressful events (Ages 21 to 26) S U M M A R Y Foundations of Research 69 Psychology 242, Dr. McKirnan Multiple independent variables Multiple IVs; summary 1 Main effect: One IV one DV Additive effects: Two IVs each have a main effect One combination has a particularly strong effect on the DV Multiple Independent Variables / Predictors tell us much more than simple main effects. S U M M A R Y Foundations of Research 70 Psychology 242, Dr. McKirnan Multiple independent variables Multiple IVs; summary 1 Main effect: One IV one DV Additive effects: Some variables may combine with others to produce very strong effects Interaction effects: One IV has a different effect on the DV depending upon another IV: Multiple Independent Variables / Predictors tell us much more than simple main effects. Emotional arousal The effect of alcohol on emotional arousal depends upon gender. IV 1: Emotional arousal IV 2: Gender Interaction: The effect of alcohol on emotional arousal depends upon gender. IV 1: Emotional arousal IV 2: Gender Interaction: Stimulation goes up if you are male. Sedation goes up if you are female. S U M M A R Y Foundations of Research 71 Psychology 242, Dr. McKirnan Multiple independent variables Multiple IVs; summary 1 Main effect: One IV one DV Additive effects: Some variables may combine with others to produce very strong effects Interaction effects: One IV has a different effect on the DV depending upon another IV: One IV has an effect only at one level of a 2 nd IV: Multiple Independent Variables / Predictors tell us much more than simple main effects. The effect of childhood abuse on risk for depression depends upon a genetic disposition. IV 1: Level of trauma The effect of childhood abuse on risk for depression depends upon a genetic disposition. IV 1: Level of trauma IV 2: 3 forms of 5-HTT genotype No genetic vulnerability: childhood trauma has no effect on depression Increasing vulnerability: More trauma greater likelihood of depression. S U M M A R Y Foundations of Research 72 Psychology 242, Dr. McKirnan Multiple independent variables Multiple IVs; summary Are critical to theory development and testing: Alcohol makes it more difficult to inhibit behavior, but primarily among men. Changing sexual risk reduction requires that we understand both peoples psychological dispositions and their drug use patterns. Stress or other environmental events can switch on genes that create psychological or other problems; genetic dispositions and environment are not separate processes. Multiple Independent Variables / Predictors: Establish key boundary conditions to theory: when and among whom does a basic psychological process operate? S U M M A R Y Foundations of Research 73 Summary Key terms: Main effect Additive effect Interaction Cross-over interaction Factorial design Repeated measure Psychology 242, Dr. McKirnan Multiple independent variables S U M M A R Y