Video Transcript
The graph below shows a series of
measurements of the air pressure at sea level. Pressure can be measured in a unit
called bar. If the true value of air pressure
on that day is known to be exactly 1.01 bar, which of the following statements
correctly describes the accuracy and precision of the data? (A) The data has both low accuracy
and low precision. (B) The data has low accuracy but
high precision. (C) The data has high accuracy but
low precision. (D) The data is both accurate and
precise.
This question is asking us to
consider the accuracy and precision of a set of pressure measurements. We’ve been given a graph with
pressure on the 𝑦-axis and time on the 𝑥-axis. For our purposes, the time at which
each measurement was taken doesn’t matter. We’re only interested in the values
of pressure that were measured. So, during this question, we’ll be
looking at where the points are on the 𝑦-axis.
To answer this question, we need to
understand what is meant by the accuracy and precision of a set of data. Let’s start by thinking about
accuracy. The accuracy of a measurement is
about how close the measured value is to the true value. If a measurement has a high
accuracy, it means that the measured value is very close to the true value. In this question, we’re told that
the true value of the air pressure is 1.01 bar. Let’s mark this true value of the
pressure onto the graph. We can see that all of the measured
points are pretty far away vertically from the line that shows the true value. So the measured values are not
close to the true value. In other words, the measurements in
this set of data have low accuracy.
Next, let’s think about the
precision of the measurements. Precision is a measure of how close
together the measurements in a data set are to each other. If the values measured are all very
close together, then the data set has high precision. If the values measured are all very
far apart, then the data set has low precision. Let’s look at the data we have been
given. We can see that all of the
pressures measured have similar values and are very close together on the graph’s
𝑦-axis. The lowest pressure measured is
1.38 bar, and the highest pressure measured is 1.43 bar, with all the other
measurements lying somewhere in between. Because these values are all so
close together, we can say that the data set has high precision.
So we have seen that the data set
has low accuracy but high precision. This corresponds to option (B). The correct answer then is option
(B). The data has low accuracy but high
precision.
