Week 5, Unit 1 Experimental Research

7/27/2019 Week 5, Unit 1 Experimental Research

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Experimental Research

Chapter 8


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Introduction

Explanatory research

Research that seeks to explain the cause of a

phenomenon, and typically asks what causes

what? or why is it this way?


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Introduction

Causal hypothesis

A testable expectation about an independent

variables affect on a dependent variable


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Introduction

Causal hypotheses and experimental designs1. Empirical association

2. Temporal precedence or time order

3. Non-causal relationship


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Introduction

Causal hypotheses and experimental

designs

Experimental designs

A study design in which the independent variable

is controlled, manipulated, or introduced in some

way by the researcher


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Introduction

The classic experiment: Data collectiontechnique or study design?

In experimental design the independentvariable is introduced, manipulated, orcontrolled

What does this mean?

The independent variable does not occur naturally,but it is the result of an action taken by the

researcher Unique feature of the classic experimental design

The researcher controls the placement of samplemembers into two or more categories of theindependent variable


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Introduction

The classic experiment: Data collectiontechnique or study design?

Ifpractical and ethical, a study can bedesigned so that the dependent variable ismeasured first and then,the independentvariable is introduced or manipulated and,finally, the dependent variable is measuredagain.

Can see whether the introduction of theindependent variable comes before changeinthe dependent variable.


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Experimental Designs

Control group

Exposed to allthe influences that the

experimental group is exposed to exceptfor

thestimulus


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Stimulus

The experimental condition of the independent variable

that is controlled or introduced by the researcher in

an experiment

The researcher tries to treat the two groups exactly

alike, except instead of the stimulus, the control

group receives no treatments, an alternative

treatment, or a placebo


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Placebo

A simulated treatment of the control group that

is designed to appear authentic


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Internal validity

Agreement between a studys conclusions

about causal connections and what is actually

true


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Experimental design

pretest-posttest control group experiment

Classic controlled experiment

An experimental design with two or morerandomly selected groups (an experimental and

control group) in which the researcher controls or

introduces the independent variable and

measures the dependent variable at least two

times (pretest and posttest measurement)


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Experimental design


Pretest

The measurement of the dependent variable thatoccurs before the introduction of the stimulus of

independent variable


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Experimental design


Posttest

The measurement of the dependent variable thatoccurs after the introduction of the stimulus or the

independent variable


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Experimental design


Probability sampling

A sample that gives every member of thepopulation a known (nonzero) chance of inclusion


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Experimental design


Random Assignment

A technique for assigning members of the sampleto experimental and control groups by chance to

maximize the likelihood that the groups are similar

at the beginning of the experiment

This can be done by flipping a coin to determine

which subject is assigned to which group

Assign each subject a number and using either a

random number table or electronic random number

generator to select members of each group


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Experimental design


Matching

Assigning members of the sample to groups bymatching members of the sample on one or

more characteristics and separating the pairs

into two groups with one group randomly

selected to become the experimental group


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Experimental design


1. The study uses at least one experimental and one

control group, selected using a strategy to make thegroups as similar as possible

2. The dependent variable is measured at least two time

for the experimental and control groups. The first

measurement is before and the second is after the

independent variable is introduced


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Experimental designpretest-posttest control group experiment

3. The independent variable is introduced, manipulated, orcontrolled by the researcher between the two measurements of

the dependent variable.4. The differences in the dependent variable between thepretest and posttest are calculated for the experimental group(s)and for the control group. The differences in the dependentvariable for the experimental and control groups are compared.


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Internal validity and experiments

Maturation

The biological and psychological processes

that cause people to change over time


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Testing effect

The sensitizing effect on subjects of the

pretest


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History

The effects of general historical events

on study participants


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Selection bias

A bias in the way the experimental and

control or comparison groups areselected that is responsible for

preexisting differences between the

groups.


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Posttest-only control group experiment

An experimental design with no pretest

Either because it is not possible to do a pretest or

because of a concern that using a pretest wouldsensitize the experimental group to the stimulus

Same design elements as other experiments:

control of manipulation of the stimulus and two or

more groups using random selection or

assignment


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Extended experimental design

Solomon four-group design

A controlled experiment with an additional

experimental and control group with eachreceiving a posttest only


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Quasi-experimental design

An experimental design that is missing one or

more aspects of a true experiment

Most frequently random assignment intoexperimental and control groups

Used when it is not ethical or practical to do a

controlled experiment


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Experiments in the field

Field experiment

An experiment done in the real world of

classrooms, offices, factories, homes,playgrounds, and the like


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Experiments in the field

Generalizability

The ability to apply the results of a study to

groups or situations beyond those actuallystudied


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Experiments in the laboratory

Laboratory research

Research done in settings that allows the

researcher control over the conditions, such as ina university or medical setting

Research examples

Hobza and Aaron Rochlen (2009)

Bushman and Anderson (2009)


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Important to evaluate a studys external

validity or the ability to generalize the

results from the laboratory to the real world


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Experiments in the laboratory External Validity Issues to Consider

1. Was the situation very artificial, or did it approximate reallife?

2. How different were study participants from otherpopulations?

3. To what extent did the participants believe that they wereup for inspection, serving as guinea pigs or play acting, orhave other feelings that would affect responses to the

stimulus?4. To what extent did the researcher communicate his or her

expectations for results to the subjects with verbal ornonverbal cues?


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Double-blind experiment

An experiment in which neither the subjects nor

research staff who interact with them knows thememberships of the experimental or control

groups.


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Natural experiments

A study using a real-work phenomena that

approximates an experimental design even

though the independent variable is notcontrolled, manipulated, or introduced by the

researcher


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Comparing Experiments to Other

Designs

Many research questions cannot be studied

using experimental design

Large samples are required

Not practical, ethical, and possible tomanipulate the independent variable

In these scenarios researchers may consider

panel, trend, cross-sectional, or case study

designs


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Summary

Study design options

Refer to Table 8.2 - Summary of Design

Studies

Issues to consider in designing a study Ethical considerations

Practicality

Time

Cost

Feasibility of controlling the independent variable


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QuizQuestion 1

An experimental design has the advantage over

non-experimental approaches of determining

the order in which events occur and

a. controlling the effects of other variables.b. minimizing the costs of the research.

c. accommodating ethical concerns.

d. proving conclusively that a relationship is

causal.


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QuizQuestion 2

In a classic experimental design, it is important

to take measures of control and experimental

groups

a. before and after treatment.b. at least once during the research.

c. after the treatment.

d. before the treatment.

e. it is not important to take measures.


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QuizQuestion 3

In experimental designs, it is important that the

control group and the experimental group

a. are as similar as possible.

b. represent very different groups so that theresearch is generalizable.

c. do not come from the same background.

d. receive the same treatment.

Week 5, Unit 1 Experimental Research

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