Measurement: Systematic versus Random Error

In any measurement, chaos, instrumental limitations, and human failings prevent perfection. This lack of perfection in measurements is called error. Some errors are random errors, meaning that they cause some of the measurements to be a little high and some to be a little low. An example of random error is the fluctuation of the readings of an electronic balance during a mass determination, which are caused by tiny vibrations, voltage fluctuations, and air currents. While random errors can be minimized, they can never be eliminated. Systematic errors are ones that cause readings to be always high or always low. These are generally due to mistakes, equipment malfunction, and poor laboratory technique. For example, reading the volume of a graduated cylinder from the top of the meniscus rather than the bottom will cause all of the volume measurements to be slightly high.

Concept Check: Many chemistry laboratory experiments instruct you to repeat the entire procedure several times and average your results. This duplication will reduce the impact of which type of error?

Answer: Performing several trials and averaging the result will decrease the impact of random error. Measurements that are slightly high should cancel out those that are slightly low, if error in either direction is equally likely.

This site was last updated 08/01/06