experimental design. types of variables independent variable (iv) ◦the thing that is intentionally...
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Example Water 10” tall Orange Juice 4” tallTRANSCRIPT
Experimental Design
Types of VariablesINDEPENDENT VARIABLE (IV)
◦ The thing that is intentionally CHANGED by the experimenter over the course of the investigation
◦ The manipulated variable
DEPENDENT VARIABLE (DV)
◦ The thing that is MEASURED or OBSERVED by the experimenter
◦ Is affected by the IV
◦ The responding variable
ExampleWater
10” tallOrange Juice
4” tall
Experimental GroupsThe values you choose for your independent variable
Example:If you are studying the effect of amount of water on plant growth, the different amounts of water given to the plants are the experimental groups: 0mL, 5mL, 10 mL, 15 mL
ConstantsFactors in an experiment that are kept the SAME and not allowed to change
Only ONE variable can be tested in a single experiment. All other variables must be held constant. Otherwise an experimenter does not know which independent variable is actually affecting the dependent variable.
Explain examples for a given experiment
Avoid BiasBias: Giving only partial information to get the results that you want
How to avoid bias?◦Repeated Trials◦Larger Sample Size◦Take Accurate Measurements
Imagine this… A weight-loss company makes a new pill that claims to help people lose 3 pounds each week. They do an experiment where they have a person, Jim, take the pills each day for a week.
Jim also recently joined a basketball league and has 2 games that week.
Jim was also sick 2 days that week so didn’t eat for 1 whole day.
At the end of the week, Jim has lost 3 pounds.
The company claims their pill is a success!!
What is wrong with this?
Repeated TrialsExperimental tests done more than onceNecessary to provide more accurate results; data is averaged togetherLessens the impact of human or chance error on the experimental results
ExampleHaving 5 plants for each group (experimental)
HypothesisFormat: If the IV, then the DV, because…
The “because” part of the hypothesis is based on your prior knowledge of scientific concepts
Example: Write a hypothesis for an experiment in which you are testing to see if the drop height of a bouncy ball affects the first bounce height of the bouncy ball
Exit Pass Carter wants to see if the amount of food he feeds a cat affects how many naps the cat takes during a 24 hour period.
Identify the IV, DV, and two constants for this experiment. Write a hypothesis for this experiment.