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Interval and Ratio Levels of Measurement

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In this tutorial, you'll learn about interval and ratio levels of measurement. These are a little confusing at first, but we'll go through the tutorial and we'll figure it out.

Interval measurements are based on an arbitrary scale. The value of zero doesn't necessarily mean that it's the bottom. An example of this would be temperature, where you can have negative temperatures. However, the intervals are still useful in that differences can be compared directly.

So here's an example. Suppose this is the Celsius scale of temperature. You may not know this, but the coldest that anything can get, the point at which atoms in a molecule cease to move, is negative 273 degrees Celsius. That's called absolute zero. Now, that's not where zero degrees Celsius is. Zero degrees Celsius is the freezing point of water. So the fact that we've placed zero here is fairly arbitrary.

Now, when we look at values other than zero, like 50 and 100 degrees, we're tempted to say that 100 degrees is twice as hot as 50 degrees. When in fact, that's not really the case. If you look at the absolute zero temperature, 100 is only a little bit further out than 50. It's not twice as far out as 50, so it's not twice as hot.

However, remember what we said before. The intervals are still useful in that we can compare differences. Meaning, the difference between 50 and 100 is the same as the difference between 0 and 50. So we can compare the differences, we just can't compare the values themselves.

By contrast, ratio measurements can compare in terms of relative distance from 0. So an example of this would be mass. Something that has a mass of 20 grams is twice as massive as something that has a mass of 10 grams.

Temperature. Now, you might say, but I thought you just said temperature didn't count. Well, you can count it if you're measuring from absolute zero.

And length, something that's 20 meters long is twice as long as something that's 10 meters long.

And so to recap, interval measurements can only accurately describe the relationships between two values using the difference between them. You can't say that a value is double the other value or half of another value, because the placement of 0 is fairly arbitrary.

And with ratio measurements, the measurement of zero is fixed, and so the values can be compared in terms of how far they are from zero. You can use the terms double, or half, or a third, or three times as far. And so the terms we used in this tutorial are interval measurements and ratio measurements.

Good luck, and I'll see you next time.