Suppose I have three dogs whose age is one, three, and five.

What is the value of \(\mu_{age}\)?

$$\mu_{age} = \frac{1+3+5}{3}=3$$

Yep. That’s simple.

Variance measures how far a data point from the mean, which can be calculated with this formula.


So, in our case, variance is calculated as follows:


Standard Deviation
Standard deviation is calculated the same as variance but with a square root.


Therefore, \(\sigma_{age} is calculated as follows:


Population Or Sample
If I were to say, “I have five dogs and pick those 3 to represent all the dogs I have,” the calculation would be a bit different.

Although the calculation is the same, mean notation is \(\bar{x}\) instead of \(\mu\)

The denominator is \((n-1)\) instead of \(n\) as an adjustment.



Standard Deviation
Yep, SD also changes.