1. Samples or groups for comparison
Controls
Samples or groups for comparison

2. Positive Control
Sample that represents the typical or unaltered procedure
“Standard”
Predictable, reliable outcome
Verifies that the procedure, materials and equipment are all working correctly

3. Negative Control Sample that leaves out the independent variable
Outcome should be predictable
Verifies that the independent variable is actually responsible for differences seen in the experimental samples

4. Validity Based on the outcomes of the positive and negative controls
If the controls give the expected results, the experiment is valid

5. Reliability A procedure or protocol gives consistent, similar results
Determined by repeated trials yielding the same results each time
Not necessarily dependent on controls or validity

6. Experimental Error
The difference between the “true” value and the measured or estimated value
Due to limitations of accuracy and precision
Does NOT include mistakes (if you make a mistake, redo it!)

7. Systematic Error Error is consistent and repeatable
Often due to equipment being miscalibrated or a mistyped or misinterpreted procedure

8. Random Error
Under the same conditions, a different value is measured every time
Unpredictable and difficult to explain