PSYB01H3 Chapter Notes - Chapter 8: Dependent And Independent Variables, Internal Validity, Null Hypothesis
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Introduction to Our Research Question
● “ Can trying to ignore a text message lead to distraction?”
● this one seems to make a more specific prediction about a type of behavior
that leads to a specific outcome.
○ As a result, our focus has moved beyond merely describing what is
taking place to identifying how one factor (ignoring text messages)
leads to changes in another factor (distraction)
● need to use experimental research to help us determine cause and effect.
Picking a Design
● We should let our question guide our design choice
● two main design types:
○ nonexperimental designs,
■ which focus on determining what happens
■ (interviews, observation, surveys)
○ experimental designs,
■ which focus on determining why something happens
Benefits of Experimental Designs
● major benefit!!!
○ ability to identify cause-and-effect relations between variables.
● first you have to establish if there is covariation between two variables
○ you must demonstrate that two variables vary or change together in a
● A correlational study cannot establish causation, but it can establish
● temporal precedence
○ when changes in the suspected cause (treatment) occur before
changes in the effect (outcome).
○ then you can establish independent and dependent variables!
● final step! prove that covariation between variables is due to independent
variable and not due to extraneous variable
○ any other factor separate from the independent variable that could
account for variations in the dependent variable.
● it has implication on your internal validity of your experiment
○ the degree to which you can rule out other possible or alternate causal
explanations for an association between the independent and
dependent variables in your experiment
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■ e.g. To show that body posturing causes changes in hormone
levels, you must demonstrate that everything except for body
posture is the same throughout your experiment.
Operationally Defining the IV: Manipulating Ignoring Text Messages
● first you have to clearly conceptualize which one is the IV and DV
● you can manipulate your independent variable by simply mimic types of
policies professors use in their course “forbidden phone checker”
○ this is an example of mundane realism
■ how closely our study parallels the real world.
■ The trick will be to make the participants’ task in our experiment
as similar to a classroom experience as possible.
● two-group design (simple experiment)
○ an experimental design that compares two groups or conditions and is
the most basic way to establish cause and effect.
Identifying the Best Groups for Our Study
● experimental group
○ whichever group gets the key treatment
● Control group
○ the comparison group that gets less of the treatment
● when choosing groups → we use all-or-nothing comparisons
○ one group receives all and other nothing lol
● to create quality groups, we want to be sure we have a high degree of
○ ability to keep everything between groups the same except for the one
element you want to test.
○ The element you want to test, sometimes called the treatment, is the
factor you think makes a difference in the outcome variable.
■ e.g. If you want to determine if 8 hours of sleep helps students’
alertness the next morning, you tell one group to go home and
sleep 8 hours that night, while you tell the other group to sleep 5
● therefore, you should put some strain on the control
group to isolate only the factor you want to examine
Group A: Not allowed to know about incoming messages; Not allowed to use the
Group B: Allowed to know about incoming messages; Allowed to use the phone
**** Because the differences between groups in an all-or-nothing approach are so
drastic, there are inevitably many unintended differences between groups. To have
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