EXPERİMENTAL RESEARCH

BUSN 364 – Week 12Özge Can

Stanford Marshmallow Experiment Measuring delayed gratification (ability to wait

in order to obtain something you want)

http://www.youtube.com/watch?v=x3S0xS2hdi4

A child is given a marshmallow and promised another, only if they could wait before eating the first one.

Researchers measure how long the child resists the temptation of eating it

Whether correlated with future success or not

Experimental Research

Builds on the principles of positivist perspective and natural sciences

(1) Starts with a causal hypothesis(2) Modify one specific aspect of a

situation that is closely connected to the cause, and

(3) Compare the outcome to what existed without the modification

Example Experiment

Manipulation of Independent Variable Question: Do suggestions affect memories? Method: Randomly assign participants to

groups and tell some participants that dreams indicate prior experience but do not tell that to other participants.

Results: Dream interpretations induce changes in memories of past events.

Conclusion: We can influence people’s memories by giving them erroneous information

Attributes of Experiments

Can powerfully test causal relationships An experiment is often artificial => includes

independent and dependent variables but exclude confounding variables

Confounding Variables: Factors that are not part of the intended hypothesis but have effects on variables of interest

Best for issues that have a narrow scope and sharpened focus

Attributes of Experiments

Isolates and targets one or a few causal variables; not effective for considering dozens of variables simultaneously

Best suited for micro-level (individuals, small-groups) more than macro-level (entire society) theoretical concerns

Practical and ethical limitations in social science experiments => We cannot manipulate many areas/conditions of human life

Power of Experimental Design Is it better to study these with a

survey or experiment?

Playing violent video games increases aggressive behavior

Students who sit at the front of the classroom make better grades than those that sit in the back

Power of Experimental Design Consider recent changes that have

been made on your campus (e.g., changes in graduation requirements or student life issues). Did the administration use experiments or quasi-experiments to determine whether or not to make these changes? Can you think of situations in which an experimental approach could have been used?

Parts of the Experiment

1. Treatment or independent variable (IV)2. Dependent variable (DV)3. Pretest4. Posttest5. Experimental group6. Control group7. Random assignment

Parts of the Experiment

Treatment => (stimulus, manipulation) the independent variable or a combination of independent variables in experimental research

Dependent variable => the outcome in experimental research. It is measured by paper-and-pencil tests, observation, interviews or physiological responses (e.g. heart beat, palm sweating)

Pretest => the measurement of the independent variable prior to the introduction of the treatment.

Parts of the Experiment

Posttest => the measurement of the independent variable after the treatment has been introduced into the experiment situation

Experimental group => the group that receives the treatment or in which treatment is present

Control group => the group that does not receive the treatment

Random Assignment

Participants divided into groups at the beginning of experimental research using a random process so the experimenter can treat the groups as equivalent

Randomness in statistical or mathematical sense: All participants have an equal chance of ending up in one or the other group

Increases our confidence that the groups do not differ in any systematic way

Random Assignment

How to Randomly Assign?

Controls in Experiment

By controlling confounding effects and isolating the effects of the treatment, we eliminate alternative explanations

Deception: Sometimes we intentionally mislead participants to control the experiment setting Deception involves using confederates and

cover stories (as false explanations) Using placebo: simulated or ineffectual

treatment intended to deceive the participants Blind studies: Single blind; double-blind

Steps in Experiment (1):

• Hypothesis• Choose a design• Design experiment– How to introduce IV– How to measure DV

• Locate subjects• Randomly assign subjects

Steps in Experiment (2):

• Gather pretest data• Run experiment– Introduce treatment– Measure DV– Gather posttest data– Debrief

• Analyze data

Types of Experimental Design Classical Experimental Design:

Includes random assignment, a control group and experimental group, and a pretest and posttest for each group

Pre-Experimental Design: Lack control group and random assignment Weaker than classical experiment Substitude classical experiments when they

are not possible

Types of Experimental Design Quasi-Experimental Design

We call them “quasi” (apparently, as if) becuse they are variations of the classical design

Some have control group and randomization but lack a pretest

Types of Experimental Design

Classical Experimental Design

Figure 8.6 Pretest-posttest control-group design.

Classical Experiment: Example

You have 40 newly hired waiters; you instruct them not to introduce themselves with first name and not to return during the meal to check on the customers

You randomly divide the waiters into two groups of 20 persons (random assignment) and send each group to one of two restaurants to begin working.

You record the amount of tips for all participants for one month (pretest score)

Classical Experiment: Example

Next, you retrain the group at restaurant A (experiment group) and instruct them to introduce themselves with first name and ask “Is everything fine?” 10 minutes after delivering the food (treatment).

You remind the group at restaurant B (control group) to continue as before.

Over the second month, you record the amount of tips for both groups (posttest score)

Internal Validity

Occurs when the independent variable, and nothing else, influences the dependent variable.

Anything other than independent variable threatens internal validity

Artifacts => unwanted or confounding variables that are due to the particular experimental arrangement

Threats to Internal Validity

Selection bias A bias that arise when groups in an

experiment are not equivalent with regard to the DV

HistorySomething occurs and affects the DV during

an experiment; is unplanned and outside the researcher’s control

MaturationNatural processes of growth, boredom, fatigue

that occur during the experiment and affect DV

Threats to Internal Validity

Testing: The very process of measuring, the pretest measure itself has an effect on DV

Instrumentation: Occurs when the instrument or measure of the DV changes during the experiment

Experimental mortality Participant fail to participate throughout the

entire experiment; they leave the experiment Demand characteristics

Participants “guess” the study hypothesis and respond to what they think the experimenter “demands” from them

Threats to Internal Validity

Diffusion of treatmentThe treatment “spills over” from the

experimental group and control group participants modify their behavior because they learn of the treatment

Compensatory behaviorWhen participants in the control group modify

their behavior to make up for not getting the treatment

Experimenter expectancyExperimenter indirectly makes participants

aware of the hypothesis or desired results

External Validity

The ability to generalize experiment findings

It addresses two major questions:

1. Can we generalize from the specific collection of participants in one experiment to an entire population => Population generalization

2. Can we generalize from what occurs in a highly controlled and artificial setting to most natural, “real world” situations => Naturalistic generalization

External Validity

Field Experiments

An experiment that takes place in the “field”; a natural setting instead of an artifical one (laboratory)

They have lower internal validity but higher external validity than laboratory experiments

Participants are usually unaware that they are involved in an experiment and react in a natural way Example: A confederate fakes a heart attack

on the subway to see how the bystanders react

Field Experiments

Helping behavior and gender http://www.youtube.com/watch?v=BuyIOM4

d-OA&feature=related

Practical Considerations

Planning and pilot testing We anticipate alternative explanations or

threats to internal validity during a good planning phase

Instructions to subjects Preparing instructions carefully so that all

participants understand the exact same thing Post-experiment interview

Ethically debriefing research participants the deception; understanding what participants thought and felt during the experiment

Online Resources:

This University of Denver site provides links to various online experiments in which students can participate.

http://www.du.edu/psychology/methods/

Watch it

Super Size Me Field experiment by Morgan Spurlock

(2004) http://www.youtube.com/watch?v=4Q-ez

COCVmg&feature=relmfu