Difference Between Positive and Negative Control

Main Difference – Positive vs Negative Control

Scientific control is a methodology that tests integrity in experiments by isolating variables as dictated by the scientific method in order to make a conclusion about such variables. It can be defined as an experiment that is designed to minimize the effect of variables other than the independent variables. (The things that are changing in an experiment are called variables). An experiment can be positively or negatively controlled. The main difference between positive and negative control is that positive control gives a response to the experiment whereas negative control does not give any response.

Key Areas Covered

1. What is Positive Control
     – Definition, Process, Uses
2. What is Negative Control
     – Definition, Process
3. What is the Difference Between Positive and Negative Control
    – Comparison of Key Differences

Key Terms: Assay, Control, Experiment, Negative Control, Positive Control

What is Positive Control

A positive control is an experimental control that gives a positive result at the end of the experiment. This type of test always gives the result as a “yes”. It is a good indication to know if the test works. Hence, positive controls are used to evaluate the validity of a test.

The positive control is not exposed to the experimental test; it is done parallel to it. The positive control is used to get the expected result. This positive result ensures the success of the test. Once the positive result is given, the test can be used for the experimental treatment. If the positive control does not give the expected result, it should be done again and again (by varying different parameters) until a positive result is given.

Figure 1: ELISA experiment – An Enzyme Assy

There are many applications of positive control in biochemical experiments.

• To detect a disease
• To observe the growth of microorganisms
• To measure the amount of enzymes present after an enzyme assay is done (in positive control, the amount of enzyme after the purification should be a known amount)

What is Negative Control

A negative control is an experimental control that does not give a response to the test. The negative control is also not exposed to the experimental test directly. It is done parallel to the experiment as a control experiment.

The negative control is used to confirm that there is no response to the reagent or the microorganism (or any other parameter) used in the test. In order to get a good result from the negative control, one should ensure that there is no net response to the test. Hence, negative controls are helpful in identifying outside influences on the experiment. For example, the effect of contaminants on an experiment can be indicated.

Difference Between Positive and Negative Control

Definition

Positive Control: A positive control is an experimental control that gives a positive result at the end of the experiment.

Negative Control: A negative control is an experimental control that does not give a response to the test.

Result

Positive Control: Positive control gives positive result

Negative Control: Negative control gives a negative result.

Response

Positive Control: Positive control gives a response to the experiment.

Negative Control: Negative control does not give any response.

Outcome

Positive Control: Positive control ensures the success of the test.

Negative Control: Negative control is used to ensure that there is no response to the test.

Uses

Positive Control: Positive control is used to test the validity of an experiment.

Negative Control: Negative control is used to identify the influence of external factors on the test.

Conclusion

Positive control and negative control are two types of tests that give completely opposite responses in an experiment. The main difference between positive and negative control is that positive control gives a response to the experiment whereas negative control does not give any response.

Reference:

 1. “Scientific Control.” The Titi Tudorancea Bulletin, Available here.
2. “Scientific control.” Wikipedia, Wikimedia Foundation, 24 Jan. 2018, Available here.