Research
Methods
for the digitally
inclined
by
Stephen R. Schmidt

Basic Methods II
Rival Hypotheses
I. Burden of Proof
II. Two Basic Research Designs
III. Threats to Internal Validity
IV. Summary
I. Burden of Proof
A. Burden of proof:
For any statement in science (psychology) lies on the investigator.
If I say that X causes Y, then it is up to me to convince you of this fact.
B. Proof requires:
That I not only show how X and Y are related, but that I show that that
relation exist with all else equal.
C. Alternative Explanations:
Demonstrating that other factors are not responsible for the observed relation
between X and Y requires that I rule out any plausible alternative explanations
of the findings.
Alternative Explanations = Rival Hypotheses
II. Two Basic Research Designs
A. Within Subjects Comparisons
Observation 1  Treatment  Observation 2
Example:
Homework  Reward
 Homework
B. Between Subjects Comparisons
Group 1 (control):
 Observation
Group 2 ( Exp.): Treatment
Observation
C. Each design has its own strengths and weaknesses.
Each design is susceptible to different threats to internal validity.
III. Threats to Validity
A. The seven mortal sins
(Catholic Church)

Avarice

Gluttony

Envy

Pride

Anger

Lust

Sloth
B. Eight mortal sins of a researcher
 each represents an alternative explanation of your results
M I S S M I T
H

Maturation

Instrumentation

Selection

Statistical Regression

Mortality

Imitation of Treatments

Testing

History
Maturation
Any systematic changes that occur over time, and are thus confounded with
the treatment.
Hypothesis:
Observe Treatment Observe
Alternative:
Observe time
Observe
Instrumentation (Instrument Decay):
Changes that occur in the measuring device (instrument) during the course
of the research that are confounded with treatment.
Hypothesis:
Observe
Treatment
Observe
Alternative:
Observe
Instrument Change Observe
Selection
Systematic differences between the comparison groups as a result of how
participants were placed in (selected for) the groups.
Hypothesis:
Alternative:
Group 1 : Control
1st subpopulation
Group 2 : Treatment
2nd subpopulation
Statistical Regression
Between a first and a second assessment, extreme scores tend to shift toward
the mean or the average.
Hypothesis:
Observe
Treatment
Observe
Alternative:
Observe
Statistical Regression Observe
Example: Give children a test of reading ability.
Select those children who score particularly low on the test (below the
mean). These children are then placed in a reading program.
After the program is over, the reading test is administered again.
How it works
An individuals scores on a test varies
from test to test.
If you specifically select participants who scored
low on a first test Ö.
Ö it is most probable that they will score higher
on the next test.
Mortality (Attrition)
Loss of research participants during the course of the study contaminate
the results.
Hypothesis:
Observe
Treatment
Observe
Alternative:
Observe
Loss of Participants Observe
Example: smoking cessation
Imitation of Treatments (carryover)
The results of a treatment effect are allowed to contaminates (carryover)
to other conditions.
Hypothesis:
Alternative:
Treatment 1
Treatment 1
Treatment 2
Knowledge of Treatment 1
Testing
Repeated measurement of the same individual may impact a personas score
on the test.
Hypothesis:
Observe
Treatment
Observe
Alternative:
Observe
Impact of first observation Observe
History
Events that take place during the course of research that influence the
outcome of the study.
Hypothesis:
Observation Treatment
Observation
Alternative:
Observation (historical event)
Observation
IV. Summary
A. The burden of proof is on the researcher to rule out alternative
explanation of results.
B. There are eight major threats to internal validity that represent
alternative explanations.
C. These can be summarized by the acronym: MIS SMITH

Maturation

Instrumentation

Selection

Statistical Regression

Mortality

Imitation of Treatments

Testing

History
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