1) The document defines key terms in research methods including variables, independent variable, dependent variable, extraneous variables, research hypothesis, and null hypothesis. 2) Variables are any characteristics that can take on different values or levels. The independent variable is what the researcher manipulates and is presumed to affect the dependent variable, which is measured. 3) The research hypothesis is the researcher's prediction about the relationship between two or more variables, while the null hypothesis states there is no relationship and gets tested statistically with the goal of being rejected.

1. Variables
A variable is any characteristic or condition
that can take on different values or “levels”
SODA TYPE GENDER ROOM TEMP
Diet Coke Diet Pepsi male female 65o 75o 85o 95o
Soda Type, Gender, and Room
Temperature are all variables because they
can take on different values or levels
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2. Independent Variable (IV)
Variable the researcher manipulates or selects
for comparison
The independent variable is presumed to have
an effect on the dependent variable
Dependent Variable (DV)
Variable that is measured
The dependent variable is presumed to be
affected by the independent variable
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3. A tip to distinguish IV and DV
Frame the question this way:
What is the effect of ________ on ________?
This will be the IV This will be the DV
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4. A tip to distinguish IV and DV
Example:
A psychologist interested in the use of imagery in
memory teaches one group of participants to make
mental images of things they are trying to remember.
She compares their memories for a list of words to the
memories of a group that does not receive imagery
training.
Reframed, it makes sense to ask:
What is the effect of imagery training on memory?
So imagery training must be the IV and memory must be
the DV.
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5. Extraneous Variables
Variables the researcher wants to control so
that they do not have an influence on the
outcome of the study.
For example, if you were conducting a taste
test between two sodas, you would want to
control:
Temperature of the soda so that both are the same
How long the soda had been on the shelf
The container, so that both look the same
Many others!
You control extraneous variables so that they
don’t impact the effect of the independent
variable on the dependent variable.
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6. Research Hypothesis
The researcher’s question and knowledge of
existing theory and previous research forms
the basis for the research hypothesis
The researcher’s prediction about the expected
relationship among two or more variables.
Example:
Reading speed will be
faster for text printed
in a large font.
Tip! In our judicial system, the prosecutor acts much like
a researcher. They begin with the research hypothesis
that “The person is guilty.”
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7. Null Hypothesis
The statement that there is no relationship among the
variables. In statistics, it actually the null that gets
tested and the researcher hopes that the results of the
statistical test will allow the researcher to reject the null
hypothesis.
Research Hypothesis: Null Hypothesis:
Reading speed will be Reading speed will not be
faster for text printed in faster for text printed in a
a large font. large font.
Tip! In our judicial system, the presumption of innocence
is the null hypothesis, “The person is not guilty.” We have
to begin with the assumption that this null is true. But the
prosecutor (“researcher”) hopes to produce enough
evidence to reject this null.
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8. Null and Research Hypothesis
More examples
Research Hypothesis: Null Hypothesis:
Children who are Children who are home
home schooled are schooled are not less
less sociable than sociable than other
other children. children.
Research Hypothesis: Null Hypothesis:
Men and women differ Men and women do
in time spent surfing not differ in time spent
on the Internet. surfing on the Internet.
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