Experimental Design Vocabulary
Any factor in an experiment that you can control, change, or measure
Variable
Marcus is testing the effect of salt on plant growth. What is his dependent variable?
Plant growth / height of plants / speed of plant growth
Number of outcomes - 1 is called
degrees of freedom
Max and Maria tested pill bugs' preference for moisture levels in their environment. They used a 3-choice chamber. How many degrees of freedom will they use in their chi-square analysis?
2
The variable in an experiment that is manipulated/changed on purpose
Independent variable
Marcus is testing the effect of salt on plant growth. Identify his independent variable.
Presence of salt
A chi-square test is a statistical procedure used to ________ data (figure out what it means)
analyze
Max and Maria tested pill bugs' preference for moisture levels in their environment. They use a 3-choice chamber and 15 pill bugs. When setting up their chi-square data table, how many pill bugs should be "expected" in each chamber?
5
The responding variable
Dependent variable
Marcus is testing the effect of salt on plant growth. Name one controlled variable.
Same amount of soil, same exposure to sunlight, same temperature conditions, (others possible)
Finding the chi-square value can be used to see if your ___________ are significantly different from your ___________
Max and Maria tested pill bugs' preference for moisture levels in their environment. They use a 3-choice chamber. One chamber has no water added, another has 5mL, another has 10 mL. What is their null hypothesis?
The pill bugs will show no preference for any particular moisture level. / There will be an equal amount of pill bugs in each chamber.
Controlled variables or constants
Marcus is testing the effect of salt on plant growth. Identify his control group.
a plant grown without salt / a plant grown with just water
If the chi-square value is lower than the critical value, what do you do with your null hypothesis?
Max and Maria tested pill bugs' preference for moisture levels in their environment. After gathering data, they do a chi-square test and find their chi-square value to be 6.32. Their critical value is 5.99. Do they accept or reject their null hypothesis?
Reject their null hypothesis
It's essential that there are controlled variables in an experiment so that we can ensure we have a _______ test.
fair
Marcus is testing the effect of salt on plant growth. What would be his null hypothesis?
Salt will not influence plant growth. / There will be no difference in growth between plants grown with or without salt.
Variations in your observed data are likely due to an influencing variable and are significantly different from the expected data if...
The chi-square value is higher than the critical value
Max and Maria tested pill bugs' preference for moisture levels in their environment. After gathering data, they do a chi-square test and find their chi-square value to be 6.32. Their critical value is 5.99. What does this mean about the significance of their observed data?
The variation in their observed results are significantly different from the expected results. There was likely a variable influencing the observed results.