# S-Cool Revision Summary

## S-Cool Revision Summary

#### Data

**There are 2 types of data:**

**Qualitative**- where the data is not numerical.**Quantitative**- where the data is numerical.

Quantitative data is the most useful set of data to us and can be in 2 forms:

**Discrete data**- can only take certain values.**Continuous data**- this set of data can take any value within a given range.

*Note:* measuring will give us continuous data whereas counting will give discrete.

#### Averages

The **mode** is the most popular value or values, i.e. the piece or pieces of data that occur most often.

The **median** is the middle piece of data when the data is in numerical order.

In general, to find the place of the median of n pieces of data we can use the following 2 rules:

- n odd - then use ½(n + 1) (the value just over halfway).
- n even - we find halfway between ½n and the next value (halfway and the next value).

The **mean** of a set of data is the sum of all the values divided by the number of values.

The mean is denoted by and for n pieces of data is calculated by:

just means the sum of all the x's - for instance, add all the bits of data together.

#### Quartiles

The **lower quartile** is the value **25% (1/4)** of the way through the distribution.

The **upper quartile** is the value **75% (3/4)** of the way through the distribution.

The **median** is the value **50% (1/2)** of the way through the distribution.

#### Standard deviation

The standard deviation gives a measure of how the data is dispersed about the mean, the centre of the data.

There are 2 formulae for calculating the standard deviation, .

Formula 1 =

Formula 2 =

The variance is the square of the standard deviation.

Variance =