Independent Dependent Variables In a science experiment the

Independent/ Dependent Variables In a science experiment, the dependent variable is the thing that is measured and the independent variable is the thing that is changed.

Independent Variable � Definition = “The cause” • The one thing that is changed in the experiment. • This variable makes one test “independent” of another test. • On a graph, it is the x axis (along the bottom)

Dependent Variable � Definition = “The effect” • The result of the experiment. • What is measured? • This “depends” on what you changed. • On a graph, it’s the y axis (along the vertical side).

How to determine Independent/Dependent Variables? Use this sentence: The independent variable (IV) causes the dependent variable (DV) to change.

Steps on how to determine Independent/Dependent variables: � � Example 1: The temperature of water was measured at different depths of the lake. Two variables: 1. temperature of water (the thing that is measured & cannot be changed by us. ) 2. depths of the lake (the thing that is changed by us– independent) � Fill out sentence with variables: � The different depths causes temperature to change.

Another Method… � -You all are “dependents” of your parent/guardian. � -You depend on them for things. � -In an experiment, ask yourself: which thing depends and changes based on the other thing? � dependent variable (DV) & independent variable(IV).

Examples: � 2. The amount of time you study will make a positive difference on your next test score. � The _____(IV) causes the _____(DV) to change. � What can you manipulate? � What “depends” on the other variable? � � Independent = time studying (you can manipulate) Dependent = score on the next test (this depends on how much you study).

Examples: � 3. Lemon trees receiving the most water produce the largest lemons. � The _____(IV) causes the _____(DV) to change. � What � � can you manipulate? “depends” on the other variable? Independent = trees receiving the most water (you can manipulate) Dependent = large lemons (this depends on how much you water the trees).

Now…your turn! �Please get into small groups and work on back of worksheet together. �Complete # 1 -12: find the independent & dependent variables. �We will go over answers in class.

And Remember… �In a science experiment, the dependent variable is the thing that is measured and the independent variable is the thing that is changed.

Independent/ Dependent Variables REVIEW � Variable = anything that changes. � Independent Variable = is one thing that you intend to change (vary) in the experiment. � Dependent Variable = the variable that changes as a result of the independent variable; what we do not know and are testing to find out.

New Terms: �Constant = a variable that does not change during the experiment, so that it could be used as a base for comparison. �Control = is what we are comparing our experiment to; our “normal” “original” item.

Example 1. Stella thinks that if people are exposed to ultraviolet light then they are more likely to get skin cancer. Stella designs an experiment wherein sample A consisted of people were exposed to ultraviolet light and sample B was not. What is the… -Control group (not manipulated in experiment) = ? -Independent Variable (manipulated in experiment) = ? -Dependent Variable (change depends on another variable) =?

And Remember… In a science experiment, the dependent variable is the thing that is measured and the independent variable is the thing that is changed.

REVIEW- key terms Variable = anything that changes. � Independent Variable = is one thing that you intend to change (vary) in the experiment. � Dependent Variable = the variable that changes as a result of the independent variable; what we do not know and are testing to find out. � Constant = a variable that does not change during the experiment, so that it could be used as a base for comparison. � Control = is what we are comparing our experiment to; our “normal” “original” item. �

Experimental & Control Group �Experimental Group = The set of objects or the group of organisms that WILL BE experimented on. �Control Group = The set of objects or the group of organisms that WILL NOT BE experimented on.

Example: � 1. Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 150 workers each and assigns each group the same task ( in this case, they are supposed to staple a set of papers). Group A is given the special juice to drink, while they work. Group B is not given the special juice. After an hour, Smithers counts how many stack of papers each group has made. Group A made 1, 587 stacks. Group B made 2, 113 stacks. � Experimental Group = the 150 workers that was given the special juice to drink. � Control Group = the 150 workers that was NOT given the special juice to drink.

Placebo � Definition = a harmless pill, medicine, or procedure prescribed more for the psychological benefit to the patient than for any physiological effect. �A placebo might be given to the control group, so that the test subjects think that they are being treated (sometimes we don’t want the control group to know they are the control group).

And Remember… �In a science experiment, the dependent variable is the thing that is measured and the independent variable is the thing that is changed.