Key Difference – Positive vs Negative Control
Scientific experiments are always performed with controls to obtain reliable results. The results gained from the experiment can be critically compared, analyzed and explained with respect to the control treatments. Therefore, it is of utmost important to maintain control experiments and they should be included into the experimental design to increase the statistical validity of the data set. There are two types of control treatments known as positive control and negative control. Negative and positive controls are defined based on the variables or the treatments of the experiment. Positive control is an experimental treatment which results in the desired effect the researcher expects. Negative control is an experimental treatment which does not result in the desired effect of the experimental variable. Thus, the key difference between the positive and negative control is, positive control produces a response or a desired effect while negative control produces no response or no desired effect of the experiment.
CONTENTS
1. Overview and Key Difference
2. What is Positive Control
3. What is Negative Control
4. Side by Side Comparison – Positive vs Negative Control
5. Summary
What is a Positive Control?
Positive control is an experimental control which gives a positive result. It does not have the independent variable that researcher tests. However, it shows the desired effect which is expected from the independent variable. Positive control is a useful proof to show that the protocols, reagents and the equipment are functioning well without any errors. If experimental errors occur, positive control will not produce the correct outcome. Therefore researcher can identify and optimize the procedure without wasting time, effort and the money. For example, when testing a plant extract for antimicrobial properties in antimicrobial compound experiment, a known antimicrobial compound containing solution is used as a positive control. It produces a prominent bacterial growth inhibition zone around the positive control disk as shown in figure 01. If you observed a prominent growth inhibition zone around the disk in the positive control, it says that the experimental setup is working well without errors.
Figure 01: Positive and negative control of an antimicrobial disk diffusion experiment
What is a Negative Control?
Negative control does not give a response to the treatment. In experiments, negative control should be designed in a way that it does not produce the desired outcome of the experiment. In the example above, the paper disk which is used as the negative control should be soaked with sterile distilled water. In sterile distilled water there is no antimicrobial compound. Hence, bacteria can grow without any inhibition. If an inhibition is observed in the negative control, it indicates that something is wrong with the experiment.
What is the difference between Positive and Negative Control?
Positive vs Negative Control |
|
| Positive control is an experimental treatment which is performed with a known factor to get the desired effect of the treatment. | Negative control is an experimental treatment which does not result in the desired outcome of the experiment. |
| Importance | |
| Positive control is an important part of an experiment. | Negative control is also an important part of an experiment |
| Reliability of the Experiment | |
| Positive control increases the reliability of the experiment. | Negative control increases the reliability of the experiment. |
Summary – Positive vs Negative Control
Controls are essential elements of an experiment. They are maintained in scientific experiments to eliminate experimental errors and biases. Results of the control experiments are useful for a validated statistical analysis of the experiment. Hence the reliability of the experiment can be increased by control treatments. There are two types of controls namely positive and negative. Positive control shows the expected effect of the treatment. Negative control does not show the effect of the treatment. This is the difference between the positive and negative controls. An experiment with controls is known as a controlled experiment. Positive and negative controls of an experiment assure that the experiment was done properly and the outcome of the experiment is affected by the independent variable.
References:
1. Weinberg, Robert A. “Positive and negative controls on cell growth.” ACS Publications. N.p., 10 Oct. 1989. Web. 04 Apr. 2017
2. Lipsitch, Marc, Eric Tchetgen Tchetgen, and Ted Cohen. “Negative Controls: A Tool for Detecting Confounding and Bias in Observational Studies.” Epidemiology (Cambridge, Mass.). U.S. National Library of Medicine, May 2010. Web. 04 Apr. 2017