EQ: How do scientists structure
experiments?
Methods of Collecting Data
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Experiments (causation)
Observations (nope)
Interviews/Surveys (nope)
Case Studies (nope)
Experiments
=
• Attempt to show a
cause/effect relationship
between two (or more)
variables.
• Trying to prove that the
independent variable (IV)
causes a change in the
dependent variable (DV).
• Anything that causes the
DV to change that is not
the IV is called a
confounding variable.
Parts of an Experiment
• Control: remains constant
• Variable: 3 quantities
that can change:
1. Independent Variable
(IV): the quantity
scientists manipulate –
what CAUSES the change
EX: “A pair of shoes
makes you jump higher.”
SHOES = the IV
2. Dependent Variable (DV): the
change you are measuring
EX: the amount higher you’ll
jump
• Both variables must be
measurable/operationalized
3. Confounding Variable (CV):
alternate causation (other than
the IV) for the change in DV
• EX: drinking Red Bull before
jumping
• Experimenter’s goal = to control
as many CVs as possible
• XY
Causality Exercises
• Identify IV, DV, CVs
• Do these pieces show causality or not?
LIVING TOGETHER LEADS TO DIVORCE
• Don’t live together if you want to stay married
– so says a nationwide study of over 2,000
couples. The study found that couples that
had lived together before getting married
were 2.3 times as likely to get divorced as
couples who had not lived together.
COFFEE PERKS UP SEX
• If you want to perk up your sex life, drink
more coffee. That’s the suggestion of a study
published recently in a leading health journal.
Researchers found that couples who regularly
drank coffee reported nearly three times as
much sexual activity as couples who did not
drink coffee. Coffee sales are expected to
increase.
SMALL COLLEGES DRIVE STUDENTS TO
DRINK
• Parents around the country are withdrawing their
children from small colleges. Their action comes
after a release of a survey last week that found
that students attending small colleges (less than
2,000 students) consumed an average of 7.2
alcoholic beverages a week. By comparison,
those attending large schools (more than 20, 000
students) consumed an average of 4.5 alcoholic
drinks. Parents speculated that the pressures of
the small college environment were pushing their
children to drink.
BAGPIPES GIVE YOU MORE THAN AN
EARACHE
• A survey has found that having a passion for
the pipes is linked to alcoholism, and can
contribute to the breakdown of players’
marriages. About 10% of players said their
hobby had ended their marriages, while 84%
knew pipers who were alcoholics.
Experiments have hypothesis
Research Hypothesis
• Expected outcome of the
study.
• A change will occur.
Null Hypothesis
• No change will occur.
By the end of the experiment, you will reject one of these hypothesis.
An experiment to measure the effects
of caffeine on stress levels
• Independent Variable
• Dependent Variable
• Research Hypothesis
• Null Hypothesis
• Possible Confounding
Variables
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Amount of caffeine present in coffee
given to participants.
Scores on a stress questionnaire.
Participants who are given a high
dose of caffeine in a coffee drink will
report higher levels of stress.
There will be no difference in the
amount of stress reported by
participants who receive a high dose
and those who receive no dose of
caffeine.
Caffeine in drinks participant has
drunk before the experiment,
feelings of stress from the
experimental situation.