# Edexcel AS Statistics revision notes

comes complete with equations

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- Created on: 06-01-12 23:42

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Statistics notes

When deciding data groups always start with the lowest value, then down round if necessary

to the nearest 5 or 2, then make sure no numbers are in the same category.

Stem and leaf Diagrams

Frequencies of data sets should be shown in brackets

If a data set is large, split the group and once you come to 5 move to the next, (universal)

For comparison you can branch out the leaves on the stem, by working backwards and

forwards, your key should reflect this.

Histograms

Used when there are gaps in data and the bars have no gaps(same numbers are adjacent)

For all histograms, imagine p-q is a data group, find and plot the lower bound of p and the

upper bound of q (endpoints).

To find the width of a bar compare both groups, for the height of a bar first work out what 1

is equal to and times it by F then divide by width

When the data intervals are equal, simply plot with x being data and y being frequency

When the data intervals are not equal, and you wish to plot the relative frequency density,

add three columns, class width, frequency density and

relative frequency density.eg.

Height 119.5-129.5 129.5-139.5 139.5-144.5 144.5-149.5 149.5-154.5 154.5-159.5 159.5-169.5 169.5-179.5

Frequency 60 80 50 93 77 67 72 54

Class width 10 10 5 5 5 5 10 10

Frequency density 6 8 10 18.6 15.4 13.4 7.2 5.4

RFD 0.011 0.014 0.018 0.034 0.028 0.024 0.013 0.010

Area under all bars=1.

To calculate a certain distribution in x, find the whole, midpoint or fractions of the groups

involved and add together. E.g to find the number of people with the heights 142cm-152cm,

notice this includes midpoint, whole and ¼, so 77 x 1/2, 67, 72 x ¼, so

38.5+67+18=123.5~124.

To calculate a distribution on a graph, add up all areas and divide this by the total freq., times

this by the f.d height and the subtraction of the two points e.g. (1333/133)*8*(90-75)

Averages

To find the median from a frequency table, F/2 (round up), then keep adding F until you

reach this number

To find the mean from a frequency table with no grouping, do XxF, do XF/F and for

grouped data, add two columns, mid-term and midtermxF then do midtermxF /F.

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