Lect 10a1 Experimental Research Experimental research is conducted to demonstrate functional (cause-and-effect) relationships An experiment must demonstrate that changes in one variable causes changes in the other An experiment must rule out the possibility that changes are caused by _____________ variables A key feature of an experiment is that a researcher manipulates a variable (the IV) and compares behavior under different __________________

Lect 10a2 Single-subject vs. Group designs ___________________: Each participant receives each level of IV and serves as his/her own control.  A functional relationship is demonstrated by comparing participant’s behavior under __________ levels of the IV ______________________: Different groups of subjects experience the different levels of the IV.  A functional relationship is demonstrated by comparing mean behavior in _______________ that received different levels of the IV

Lect 10a3 Types of Group Designs 1. ________________________ (subjects) design. The experiment compares groups that receive_____ different levels of the IV.  e.g., Memory is studied in 2 groups who have been given auditory or visual stimuli 2. Between-group (subjects) ________________ design The experiment compares groups that receive _____ or more different levels of the IV.  e.g., Classical conditioning is studied in 3 groups who have been short, moderate, and long delays between the CS onset and US onset.

Lect 10a4 Between-subjects two-group design (___________________________) Sample Drawn Randomly from Population Random Assignment of Participants to Conditions Measurement of the Dependent Variable IV=Level 1 IV=Level 2 e.g., Compare effects of low or high-anxiety on tendency to seek the company of others (Schachter, 1959) (33%, 63%)

Lect 10a5 Between-subjects, multilevel design (_______________________________) Sample Drawn Randomly from Population Random Assignment of Participants to Conditions Measurement of the Dependent Variable IV=Level 1 Measurement of the Dependent Variable IV=Level 3 Measurement of the Dependent Variable IV=Level 2 e.g., The effects of electroconvulsive shock on learning when shock is delivered 10 s, 1 min, 10 min 1 hr or 3 hrs after learning. (Pinel, 1969)

Lect 10a6 Multilevel designs give your ______________: (i.e., may show that effect is really ___________)

Lect 10a7 Why would you use a group design? Some questions ________________ with a single- subject design  e.g., effects of experiences early in life on speed of learning later in life IV is a ________ variable (can’t do a real experiment)  e.g., comparing impulsivity in women with and without borderline personality disorder Experience under one level of the IV may affect what people do at __________________  e.g., investigating the effects of attractiveness on criminal sentencing

Lect 10a8 Group Design Features 1. Participants are often _______________ from a population to create a representative sample Random selection – each member of population has ________________ of being selected Promotes ___________ validity

Lect 10a9 Main threat to internal validity of between- group designs: You want your two groups to be as similar as possible or _____________ There may be _____________ in age, gender, socio- economic status, intelligence, personality across participants in your two groups. If participants in one group differ than those in another then the _________________________ and not the IV may affect the results This internal validity threat is called ________________ How do you control for this?

Lect 10a10 2. Participants in the sample are then_________ ___________ into groups. Random Assignment: each participant has an equal chance of being assigned to a group. Why? Spread individual-difference factors ________________ Group Design Features

Lect 10a11 Defined Population of Interest Sample RANDOM SELECTION & ASSIGNMENT _________________ Group 2 Group 1 __________ ____________ _________ ____________

Lect 10a12 Group Equivalence: What if you are concerned that differences in one variable across groups may confound your results? You may also ______________________ or restrict it if you think it may influence performance You can use participant _________. _____ of participants are grouped together based on some trait and then each one of the pair is randomly ______________ to one of the groups.

Members of sample are randomly assigned to groups): Mean = 100 Groups after Random Assignment:

Mean = 94Mean = 106 Groups after Random Assignment: Members of sample are randomly assigned to groups):

Sample: Groups after Matching Mean= Matching: = = = = = = = = Random Assignment of Pair members: = = = = = = = =

Lect 10a16 Defined Population of Interest Sample RANDOM SELECTION & ASSIGNMENT Generalization Group 2 Group 1 Random Selection Random Assignment of member of pairs _______________

Lect 10a17 Problems with matching Lots of ______ Cannot ensure group _____________  Can’t match on ____ variables  Can only match on variable _________________ What if some subjects __________?

Lect 10a18 3.Each participants is exposed to only _____ condition 4.Groups should be treated ____________ (except for the IV) 5.Every member of a group is treated the same way – no ______________ treatment Between-Group Design Features

Lect 10a19 6.______________ statistics (e.g., ANOVA, t-tests) are used to evaluate the data 7._____________ sample size (n) 8.Experimental control obtained when you see different ___________________ Between Group Design Features

Lect 10a20 Analysis of Data in Between-Group Designs Between subjects (group) design, two independent groups:  ______ for independent groups Between subjects (group) group design, two matched groups:  ______ for dependent groups Between subjects (group) multilevel design:  _________