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Question Video: Determining the Difference between Accurate and Precise Measurements Chemistry

Which of the following statements describes the difference between accurate and precise measurements? [A] Precise and accurate measurements have the same meaning. [B] Precision is how evenly measurements are spread apart from each other, whereas accuracy is how close measurements are to each other. [C] Precision is how close measurements are to each other, whereas accuracy is how close measurements are to the true value. [D] Precision is how close measurements are to the true value, whereas accuracy is how close measurements are to each other. [E] Precision is how many measurements are needed to obtain an accurate measurement.

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Video Transcript

Which of the following statements describes the difference between accurate and precise measurements? (A) Precise and accurate measurements have the same meaning. (B) Precision is how evenly measurements are spread apart from each other, whereas accuracy is how close measurements are to each other. (C) Precision is how close measurements are to each other, whereas accuracy is how close measurements are to the true value. (D) Precision is how close measurements are to the true value, whereas accuracy is how close measurements are to each other. (E) Precision is how many measurements are needed to obtain an accurate measurement.

Before we dive in to exploring the difference between accuracy and precision, let’s clear these answer choices so that we have some screen space. Accuracy is how close a scientific measurement is to the correct value. Precision is how close scientific measurements are to each other. Let’s say we’re throwing darts at a dartboard. We often use a dartboard to illustrate the difference between accuracy and precision. The center of the dartboard represents the correct value. If we throw a dart and it hits the center of the board, our aim was accurate. But if we throw a dart and missed the center of the board, that is not accurate.

Next, we throw three darts that land close together on the board. Since these three darts are close together, our aim was precise. Next, we throw three more darts at the board which don’t land anywhere near each other. This means our aim this time was not precise. Notice that precision and accuracy don’t have to occur together. The three darts that are precise are not near the center of the board, which means even though our dart throwing for these three darts was precise, it was not accurate.

Now that we know the difference between accuracy and precision, let’s apply this to a scientific measurement. For example, we might be measuring the volume of an aqueous solution using a graduated cylinder. We need several 15-milliliter samples of the solution. If we measure out samples of the solution and all of the volumes are around 15 milliliters, our measurements are accurate because 15 milliliters is the correct value. Our measurements are also precise because they are all close together. If we measured our samples and all of them had a volume of around 16 milliliters, our measurements would be precise because they’re close together but our measurements would be inaccurate because they’re not close to the correct value.

We also might take measurements that are like this. In this case, our measurements are not close together, so they are not precise. But all of the measurements average to 15 milliliters, which is the correct value. So they are accurate. Or we could measure out the samples, and the volumes are all over the place. In this case, our measurements are not accurate or precise because our measurements are not close to the correct value and they’re not close to each other.

There are a number of reasons why our measurements might not be accurate or precise. For example, the glassware might not be correctly calibrated. This could result in all of our measurements being inaccurate. Or the glassware might be correctly calibrated, but we are not reading the volume correctly. For example, we might take the measurement looking at the graduated cylinder from different heights, which could cause our measurements to not be precise.

Now that we’ve explored the difference between accuracy and precision, let’s bring back the answer choices and finish up this question. As we’ve learned, accurate measurements are close to the correct value, whereas precise measurements are close to each other. So the statement that describes the difference between accurate and precise measurements is answer choice (C). Precision is how close measurements are to each other, whereas accuracy is how close measurements are to the true value.

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