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I don’t understand the following quote from the lesson:
“By finding the number of standard deviations a data point is away from the mean, we can begin to investigate how unusual that datapoint truly is. In fact, you can usually expect around 68% of your data to fall within one standard deviation of the mean, 95% of your data to fall within two standard deviations of the mean, and 99.7% of your data to fall within three standard deviations of the mean.”
Take for an example of a group of 100 people and their height. Let’s say we calculated the mean height of these 100 people to be 180 cm and the standard deviation of heights for this group to be 15 cm. This is often written as 180 +/- 15 cm .
So within one standard deviation we have 68% of our data. This would be anyone between 165 and 195 cm high (180 - 15 cm) and (180 + 15 cm). So we can expect 68 % of our group to be within this range. Within two standard deviations is just doubling the value, so 15 would be 30.
You could now say that roughly 95% of the group have a height between 150 and 210 cm since we’re within two standard deviations (180 - 30 cm) and (180 + 30 cm).
It should be noted this is really dependent on having a fairly normal distribution. The following links have more info if that isn’t clear-
) below.
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