Positive Control: Definition & Experiment

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  • 0:00 Definition of Positive Control
  • 1:05 How Does a Positive…
  • 1:56 Benefits of Positive Control
  • 2:54 Lesson Summary
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Lesson Transcript
Instructor: Adrienne Brundage
A positive control is a part of good experimental design. A positive control receives a treatment with a known response, so that this positive response can be compared to the unknown response of the treatment.

Definition of a Positive Control

Doctors and other scientists use experiments to determine if things like drugs actually work the way they are supposed to. An experiment is an orderly procedure used to test the outcome of a particular set of circumstances, like if a drug really works. Let's look at how doctors figured out if aspirin really cures headaches. The doctors gave aspirin to someone with a headache and observed if it went away. But how do they know the aspirin actually caused the headache to go away? This is where controls come in.

Experiments have two major groups: the test subjects and the control subjects. The test subjects are the individuals that are being used to check what happens when something changes. The test subjects in the headache experiment would be those people with headaches who take aspirin. The control subjects are those individuals that don't get access to whatever is being tested. They are used to compare the test results. One major type of control subject is the positive control. A positive control receives a treatment or test with a known result. This result is usually what researchers expect from the treatment, so it gives them something to compare.

How Does a Positive Control Work?

Let's go back to our headache experiment. A doctor wants to cure a headache, and heard that aspirin helps. She decides to test and see how effective aspirin actually is at curing headaches. So, she finds a group of people with headaches and gives them some aspirin. But wait - how does she know that it was the aspirin that actually cured the headaches? I've had plenty of headaches that just go away on their own.

A good experiment needs something to compare the test results to. So, the doctor goes and finds another group of people with headaches, and gives them something that she knows will cure the headache. She then observes how quickly the headaches go away and how many headaches the known drug cured. She now has something to compare the aspirin to. This is how we get all that information in drug advertisements that say things like 'aspirin works twice as fast as other drugs!' The positive control gives scientists a known to compare to the unknown test.

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