# MDM4U Measures of Spread; Gizmos 2016-05-09

We learned about standard deviation today! It’s a way to measure how spread out your data is.

For example, if you have a data set with a mean of 10, a mode of 10, and a median of 10, you don’t know a lot about the values. You know a lot about the middle, but not the edges.

Standard deviation is a measure of how spread out the values are. Variance is another measure that we don’t use much in this course (it’s the square of standard deviation). We’ll learn more about how to use and interpret the standard deviation, so that’s enough to go on for now.

For notation, we use different symbols for mean, standard deviation, and variance depending on whether we’re talking about a population or just a sample.

Population Measure Sample
$\mu$ mean $\overline{x}$
$\sigma$ standard deviation $s$
${\sigma}^2$ variance $s^2$

We also used two Gizmos! from explorelearning.com: the Real-Time Histogram and the Sight vs. Sound Reactions. If you weren’t here, ask me tomorrow for the class enrollment code (I can’t post it here).

Also, see if you can beat my score for Sight ReactionÂ (that is, have a lower mean and/or a lower standard deviation):