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Psy2005: Applied Research Methods & Ethics in Psychology

Lab Week 7: Using Simple Effects to investigate the effects of type of session and type of therapy on self-reported drug

use

SPSS data filesOpen Psy2005 folderOpen Week 7Double click on ‘drug treatments3.sav’Fundamental principle

◦Each participant has their own row◦Each different bit of data must go in a

separate column / variableData view vs. Variable View

◦Change via ‘tabs’ at bottom of window or keyboard combination ⌘T

◦Data view for viewing / editing data◦Variable view for details of variables

Tutor Led

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Aims & OutcomesProvide an overview of research

focusing on drug treatmentsConduct a Simple Effects analysis

on an independent groups factorial ANOVA◦Session when treatment is held

constant◦Treatment when session is held

constantExplain the key features of Simple

Effects

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Work on your own, in groups, whatever you feel is best for you!

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Drug Treatments in Current StudyTreatments (Weekly Sessions)

◦12-Step programme◦A Cognitive–Behavioural Motivational

Intervention ◦Standard care

Type of session◦Group therapy◦Individual therapy

Outcome Measures (1, 6, & 12 months)◦Self-monitored logbooks: drugs taken◦Recordings taken over a 28 day period prior to

measurement

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Participants & TherapistsParticipants:

◦Prolific and other Priority Offender status and tested positive for cocaine or heroin during their arrest.

◦Randomly allocated to one of the three groups.

Therapists: Twelve therapists ran the sessions. ◦All were qualified to degree standard

and had a minimum of three years experience

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ProcedureParticipants took part as part of a

voluntary rehabilitation procedureParticipants had either:

◦ 90 minute weekly closed (nobody was allowed to join after the first session) meetings in groups of 4-8 people with two Counsellors.

◦ 45 minute weekly individual sessions with one Counsellor

Participants attended the sessions for 1 year. Treatment outcomes were measured at 1 month, 6 months & 12 months.

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About the Experiment!Teasing apart the design

◦Independent variables: Type of drug treatment : 12 Step,

CBT/MI, Standard Care Type of session: group, individual

◦Dependent variable Self-reported drug use

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Factorial ANOVA

Total Variability

Variance Explained by the Experiment

Variance explained by

treatment

Variance explained by session

Variance Explained by interaction

between treatment and session

Unexplained Variance

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Self-reported drug use at time: 1 month

Self-reported drug use at time: 6 months

Self-reported drug use at time: 1 Year

Type of session:Group Vs Individual therapy Situation. More on this later!

Type of therapy:12 StepCBT with MIStandard care.

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Conducting a factorial ANOVAStudent Led

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Student Led

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The Output: The ANOVA

Session (F(1,136)=10.352, MSe=1.650, p=0.002)

Therapy (F(2,136)=13.550, MSe=1.650, p<0.001)

Session x Therapy (F(2,136)=4.402, MSe=1.650 p=0.014)

Tutor Led

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The Output: The interaction effect(F(2,136)=4.402, MSe=1.650, p=0.014)

Tutor Led

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Conclusions: This is your first Summative Assessment

Following a Factorial ANOVA on Drug Use (1 month) the following findings were observed◦ Main effect for Session Factor◦ Main effect for Treatment Factor◦ Interaction effect for Session x Therapy

What does this mean?◦ You will have to wait until Week 8 to get a better

understanding of the interaction.◦ Before then, look at the graph and try to make

sense of it yourself◦ You need to understand this as it forms an integral

part of your first summative assessment

Tutor Led

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Evaluating the interaction effect: Simple Effects

• Interpreting main effects:• Does the factor have a similar effect at all levels of the

other factor• Are the lines parallel?

• Interpreting interaction effects: • A statistical interaction occurs when the effect of one

independent variable on the dependent variable changes depending on the level of another independent variable.

• Simple Effect analysis is the examination of the effect of one factor at all levels of the other factor

• For our example there are two simple effects for type of treatment (more if they are significant!) and three simple effects for type of session.

• We will use the error term from the main ANOVA as our denominator as this is the most accurate measure of unexplained variance (MSe=1.650, df=136)

Tutor Led

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Simple Effects for type of Session: Plotting the analyses

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2.

3.

Session:1. group vs individual at 12

Step2. group vs individual at

CBT/MI3. group vs individual at

Stan. Care

Tutor Led

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Back to SPSS: Select Cases for 12-step participants Student Led

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Select Cases for 12-step participants

Student Led

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Independent Groups ANOVAStudent Led

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Output for Session at 12-Step

Apply a Bonferroni correction as we are carrying out a family of tests (0.05/3=0.0167)

Session at 12-Step (F(1,136)=14.596, MSe=1.650, p<0.001) These findings show that there is a significant reduction in self-reported

drug use when the 12-step was presented in group sessions as opposed to individual sessions

This is replaced With MSe=1.650

This is replacedWith df=136

This becomes 14.596

Student Led

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Back to SPSS: Select Cases for CBT/MI participants Student Led

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Select Cases for CBT/MI participants

Student Led

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Intependent Groups ANOVAStudent Led

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Output for Session at CBT/MI

Apply a Bonferroni correction as we are carrying out a family of tests (0.05/3=0.0167)

Session at CBT/MI(F(1,136)=4.584, MSe=1.650, p=0.034) These show that the group session is more effective at

CBT/MI but the correction means we cannot accept these findings as significant

This is replaced With MSe=1.650

This is replacedWith df=136

This becomes 4.584

Student Led

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Back to SPSS: Select Cases for Standard Care participants Student Led

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Select Cases for Standard Care participants Student Led

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Intependent Groups ANOVAStudent Led

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Output for Session at Standard Care

Apply a Bonferroni correction as we are carrying out a family of tests (0.05/3=0.0167)

Session at CBT/MI(F(1,136)=0.135, MSe=1.650, p=0.714)

These show no significant differences between the two types of session at Standard Care

This is replaced With MSe=1.650

This is replacedWith df=136

This becomes 0.135

Student Led

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Simple Effects for type of Session: Plotting the analyses

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2.

3.

Session:1. group vs individual at 12

(F(1,136)=14.596, MSe=1.650, p<0.001)

2. group vs individual at CBT/MI (F(1,136)=4.584, MSe=1.650, p=0.034 NS)

3. group vs individual at Stan. Care (F(1,136)=0.135, MSe=1.650, p=0.714 NS)

Tutor Led

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Workbook 1 (Week 7)

There is no Workbook 1 (week 7) but please make sure you take a copy of the PPT files as they contain all of the information you need to write your lab report.