Video Transcript
The following image shows the position of three points on a set of target boards. The true value is represented by the center of the target, the red circle. Which target board shows poor accuracy but good precision?
Accuracy describes how close a measurement is to a true or accepted value, while
precision describes how close measurements are to each other. A set of measurements may be accurate or precise, accurate and precise, or neither
accurate nor precise. Let’s consider two students that each performed an experiment to measure the density
of aluminum. Student A’s data is shown on the left and student B’s data is shown on the right. The true or accepted value for the density of aluminum is 2.70 grams per centimeter
cubed. We can see that each of Student A’s measurements is close to the true value. So these measurements can be considered accurate. In addition, the measurements are quite close to one another. So we can also consider the measurements to be precise.
In contrast, student B’s measurements are not close to the true value and they are
not close to each other. So student B’s measurements are neither accurate nor precise. With this in mind, let’s return to the question. We are looking for a target board that shows poor accuracy and we are told that the
true value is represented by the red circle. So a target board with poor accuracy will have points that are not close to the red
circle. This means that we can eliminate answer choice (B). But we also want the target board to show good precision. This means that the points will be close to each other.
We see the points on target board (C) are close to each other but not close to the
red circle. Thus, the target board that shows poor accuracy but good precision is target board
(C).
Which target board shows good accuracy and good precision?
Good accuracy means that the points will be close to the red circle, the true
value. And good precision means that the points will be close to each other. The target board that shows the points close to each other and close to the red
circle is target board (B). Thus, the target board that shows good accuracy and good precision is target board
(B).
Which target board shows poor accuracy and poor precision?
Poor accuracy means that the points are not close to the red circle, the true
value. And poor precision means that the points are not close to each other. The target board that shows the points far from each other and far from the red
circle is target board (A). Thus, the target board that shows poor accuracy and poor precision is target board
(A).
