EQ: How do scientists structure experiments?

Methods of Collecting Data

• 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.

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Parts of an Experiment

• Control: remains constant• Variable: 3 quantities

that can change:1. Independent Variable (IV): the quantity scientists manipulate – what CAUSES the changeEX: “A pair of shoes makes you jump higher.” SHOES = the IV

2. Dependent Variable (DV): the change you are measuringEX: 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

• 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.