Video Transcript
Which of the following statements most correctly describes how systematic measurement errors affect the accuracy and the precision of measurements? (A) Systematic errors decrease measurement accuracy. (B) Systematic errors decrease measurement precision. (C) Systematic errors decrease both the accuracy and the precision of measurements. (D) Systematic errors do not affect measurement accuracy or measurement precision.
Clearing some room at the top of our screen, let’s remind ourselves of what a systematic error is. When we’re making a measurement, if there is something that’s basically off about some part of that process, perhaps an uncalibrated measurement tool or an incorrect assumption we’re making, that can lead to a mismeasurement, an error, in every one of the measurements we make. For example, say that we wanted to measure a person’s mass and we did this by having the person step onto a scale. If that person for some reason decided to carry a five-kilogram mass while they were on the scale, then that would lead to a systematic error in the measurements of the person’s mass. Even if everything else about the experiment was set up correctly, the values read out for the person’s mass would always be about five kilograms too much.
Using this example, let’s think about just how this systematic error may affect the accuracy and the precision of the measurements of this person’s mass. We’ve seen that whatever the actual mass of this person, by holding a five-kilogram mass, the reported mass values for the person will be high. We see then that this systematic error will decrease the accuracy of our measurements. That is, it will make them tend away from the true value of the person’s mass.
Next, let’s consider the effect of a systematic error on measurement precision. Precision has to do with the uncertainty in our measurement device. This scale, for example, may be able to measure masses, say, to the nearest kilogram. The fact that the person on the scale is holding this five-kilogram mass will not affect the scale’s uncertainty. Therefore, this systematic error will neither increase nor decrease the precision of the measurement. These findings, it turns out, are generally true for systematic errors. As described in answer choice (A), systematic errors decrease measurement accuracy. We can’t say that systematic errors have any effect on measurement precision, so our best answer to this question is option (A).
