Independent & Dependent Variables

*This is an excellent video that goes over Independent and Dependent Variables, and it explains why we need to only change 1 variable at a time.

Here's another great video showing the differences between independent and dependent variables:

1) The 1 thing we test, change, or is different between groups in an experiment is the independent variable (we control it!)

2) What we measure or observe at the end is the dependent variable. It's the data we collect.

3) Constants (controlled variables)- Variables that are kept the same, do not change.

TIPS:

Independent variable- "I" change it.

Dependent variable- depends on the independent variable.

Think of Cause (IV) and Effect (DV). The IV comes first (the cause) and the DV comes after (the effect).

So when writing a Hypothesis, the format should be: If the (independent variable) changes, then the (dependent variable) will change because...

Click on the picture below to see it bigger:

Remember, the ONLY variable we change in an experiment is the independent variable. Scientists control all other variables so they can be sure that the results are caused by the independent variable only! This is called a controlled experiment. And it allows the experiment to be fair.

Also, you need to repeat an experiment several times to make sure your results are reliable or valid (accurate).These are called trials. If you do an experiment just 1 time, you might make a mistake or get a strange result.

More Vocabulary:

1) Experimental group- the group that is tested or receives the change.

2) Control group- the group that is not really being tested (gets no special treatment). It's the standard, used for comparison only.

3) Sample size- the total number of people/animals/plants being studied in an experiment. 

4) Placebo- a fake pill that contains no active ingredients but is used as a control in testing how well another, real pill works.

5) Trials- the number of times you do a test in an experiment. The more trials you do, the more reliable the experiment is.

*A control group is used to see if the change actually works (compared versus the experimental group).

*A large sample size is better for an experiment because your results will be more reliable or accurate since you have more data to count on.