Designing Your Own Experiment

(follow along on your sheet)

EXPERIMENTAL DESIGN Your Mission: Design an experiment to determine if a new drug will

reduce ADHD in children.

DRUG INFLUENCES HYPERACTIVITY

Independent Variable Dependent Variable

(Cause) “will lower” (Effect)

Must have two groups to compare…

1) Experimental 2) Control Group

Gets the Drug Does NOT get the Drug

How will be operationally define hyperactivity? (How will you measure it?)

- Measure the number of students of get out of their seat in school.

Our Results:

-Kids who took the drug were hyperactive 25% of the time.

-Control group (did not take drug) were hyperactive 50% of the time.

Are there any other variables that could have caused these results?

YES!!! These are called CONFOUNDING VARIABLES.

What are the confounding variables in our experiment?

Have to go to the bathroom, weather, time of day (morning, after lunch), attitude or expectation, sleepy

How do we eliminate these confounding variables?

Make it double blind and use a placebo with your control group.

What else can we do to make this experiment better and account for individual differences?

RANDOM ASSIGNMENT!

-Assign students to groups randomly.

-Need to have about 20 students in each group for a good experiment.

-No random assignment = “Quasi” experiment that is flawed

How do we know our results are statistically significant?

-Use statistics to find standard deviation & P-value.

-Remember, the P-value must be .05 or less!

An Experiment tries to isolate cause by controlling as many confounding variables as possible.

Correlation (relationships) Experiment (cause & effect)

Let’s Try Another One!

Does drinking coffee cause higher levels of anxiety?

EXPERIMENTS The only way to show CAUSE and EFFECT

Your Mission: Design an experiment to determine if coffee will increase a person’s level of anxiety.

HYPOTHESIS – Inference that predicts cause & effects relationships.

The consumption of coffee produces higher levels of anxiety.

What are you studying and how are you going to measure it?

FOCAL BEHAVIOR – The behavior you are testingAnxiety DEFINE OPERATIONALLY – How are we measuring

statistically the behavior we’re studying? Must remove all opinions and use only things that can be reported or observed.

Scale of 1 to 10 that each participant uses to rate their level of anxiety when they come in and after they drink coffee.

Could also use heart rate.

Determining Your Variables

INDEPENDENT VARIABLE – Factors in an experiment that the scientist changes to cause a desired behavior.

Amount of Coffee (0 cups, 2 cups, 4 cups)

 

DEPENDENT VARIABLE – Desired effect that depends on the independent variable.

Level of Anxiety

 

How can I pick out the independent variable from the dependent one in an

experiment? Ask yourself:

Does coffee cause anxiety? Or Does anxiety cause coffee?

Take the one that makes sense, and know that the variable that causes the other variable is always the independent variable. (Coffee is the independent variable in this experiment so anxiety must be the dependent variable).

CONTROL GROUP – The group that you compare your results to. They are not effected by the independent variable.

Non-coffee drinkers CONTROL ALL ASPECTS – Must eliminate alternative

causes for the behavior you are studying by controlling all aspects of experiment. This way we can be certain there is no third cause of the behavior other than the one we’re studying.

Environment must be the same, Must not have drank coffee before they arrived for the testNo outside stressors.

EVIDENCE – Must come from systematic and controlled observations that are measured statistically and comparisons NOT our own interpretations or opinions of events because these are biased and subjective. Afterwards, organize the evidence using statistics.

Was there an increase in anxiety after they drank coffee? Was it higher with the more coffee that was drank? Look to our anxiety scale to see this.

 REFORMULATE HYPOTHESIS – Check your hypothesis to

see if the evidence supports it. REPEATABLE – Must have another scientist repeat your

experiment and prove your findings true by getting similar results.