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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…

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Take the X and for the median position, X x ½, for upper quartile position X x ¾, for
lower quartile position, X x ¼ and for interquartile range, upper quartile-lower quartile.

Always add a cumulative
frequency column to data, use
this to find values that fall into…

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Variance and standard deviation
Variance is a measure of spread and the
average of the squared distances from the median, standard deviation
is the square root of variance, look at equations below:

X X midpoint F Fxmidpoi Fx(midpoint
nt )

For non-frequency table data For frequency
table data Where…

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Comparing distributions
Mention one measure of spread and
one measure of average or centre in


Probability experiment: has outcomes that occur at random
Experimental probability: e.g. throwing a die 100 times, getting 5 14 times 14/100=0.14
Theoretical probability: if a fair die was thrown, P(getting 5)= 1/6= 0.1616...…

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Using the mean of x and y, quadrants can be found on a graph and are numbered
anticlockwise from the right, so correlation is positive if plots are in quadrants 1st and 3rd
Summary statistics are used to calculate PMCC;

This shows the strength of the correlation, below shows…

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For cumulative distribution function, anything over the scale=1, and
F(X)= accumulating the probabilities, the last should be 1 (use this to equate functions)
To find the probability of an x term not given, round down, if there is a whole number minus
form it the previous number's probability.
The mean…

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