Formulae and key words

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  • Created by: Nia
  • Created on: 09-04-12 11:56


Quantitative variables = numerical observations

Qualitative variables = non-numberical observations

Discrete variable = specific values in a given range

Continuous variable = any value in a given range

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Mean, mode and median in a set of data

Mode = value that occurs most often


middle value when the data is put in order

(n+1)/2 gives the place of the median value


Sum of all observations divided by the total number of observations


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Mean, mode in frequency distribution tables and gr



To find the mean and median its helpful to add a column for the cumulative frequency

Grouped data

in grouped data x = the midpoint

modal class = class with highest frequency

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Median in grouped data

Interpolation must be used


(see page 21 in edexcel)

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Quartiles and range and percentiles

Range = difference between highesh and lowest value

Quartiles = split data in to four parts eg. lower quartile (Q1) = n/4

Interquartile range = Q3-Q1

Percentiles = split data in to 100 patys

xth percentile = Px = xn/100

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