**Statistics** designed to answer questions such as central tendency, spread/variability, extreme values are called **summary statistics**.

This **recipe** includes the following topics:

- Mean
- Variance and Standard deviation
- Effect Size
- Cohen’s d

### Mean

**Mean**is the most common summary statistic used to describe the central tendency of the distribution.- Useful when samples are pretty
**similar**. Eg: Size of an apple in a supermarket are mostly similar.

### Variance and Standard deviation

**Variance**is a summary statistic often used to quantify spread.**Standard deviation**is the square root of variance, also used as a measure of spread.- Useful when samples
**vary**widely. - Eg: Pumpkin can weigh between 1lb to 400lb. Both mean and variance may be needed to describe the distribution.

### Effect size and Cohen’s d

- Effect size is a summary statistic intended to quantify the size of an effect.
- Eg: Size of an effect in two groups where Group A was given Medicine A but Group B was given none.
- Cohen’s d is intended to measure this effect size.