## Representing Data - Measures

## Quartiles

Quartiles are the

**quarter values**. They are**Q1, Q2 and Q3**.**Q2 is the median****Q1 = n/4**

Q2 = n/2

Q3 = 3n/4

In grouped data you use interpolation.

Q2 = n/2

Q3 = 3n/4

Youstill calculate in the same way as in representing data - location except the quartile position is different and all the other values come from this position

The

**Interquartile range**is

**Q3 - Q1**

## Percentiles

Percentiles split the data into

**100 sections**

The xth percentile (**Px**) is the**xn****th term**

100

The100

**interperceptile range**from x% to y% is**Py - Px**## Variance and Standard Deviation

The standard deviation is the mean deviation of a number from the mean

The variance is the standard deviation squared

**Standard deviation**is given the symbol**σ**The variance is the standard deviation squared

The equation for standard deviation is:

## Coding

Same as in location except

E.g.

y = 10x - 3

Coded standard deviation = 14.1

Standard deviation = 1.41

**subtraction or addition don't affect standard deviation**E.g.

y = 10x - 3

Coded standard deviation = 14.1

Standard deviation = 1.41