# Numerical Measures Notes (simple!!) eg mode, median, IQR - Statistics - S1 - AQA - A Level

easy methods to find the mode, median, range, iqr

AQA S1

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- Created on: 30-04-12 22:05

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Statistics - Numerical Measures

Calculating Averages

Mode - simply find the value which occurs the most, non calculator

Median - put values into order and cross off outer values, working your way towards the middle, non

calculator. If there are two middle values, add them together and divide by 2. Tip - can be given

unknown values, but the shouldn't affect median if they are extreme

The median is:

n+1

Odd number of values? 2 th term

n n

Even number of values? it is the average of the 2 th and 2 + 1 th terms

Mean - it is the sum of the values, divided by the number of the values. Type all the values into the x

column in the table in your calculator, type 1 in the frequency column and then find your mean, x.

Easy

Calculating Measures of spread

Range - simply the difference between the highest and lowest values

Interquartile range - is the difference between the upper and lower quartiles. Find the median, then

find the median of both sides (left and right.) Q3 - Q1 = IQR

If you're reading data off a table, then these are the formulas you need:

Q1 = n+1 th term

4

Q2 = n+1 th term

2

3(n+1)

Q3 = 4 th term

Standard deviation - is a measure of the average deviation of values from their mean. Should never

be negative because it is based on the sum of squares. Type all the values into your x column in your

calculator and type 1 into your frequency column, then find the standard deviation, x n-1

Variance - is standard deviation squared

Frequency distribution - use the same method as standard deviation, but enter the correct values

into the frequency column

Estimating (only applies to grouped frequency distribution)

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