Topic 1: Organizing Data

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  • Created on: 16-03-15 19:02
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1|Organising data
Raw data ­ the data collected
Stem and leaf diagram ­ single data or back-to-back data
5|468 means 54,56,58 730 |2means 20,23,27
Always use a key
Discrete data ­ possible values are separated by gaps , eg 1, 1.5, 2, 2.5,...
Continuous data ­ comes from measurement, eg 29.8, 29.9, 32.0, 24.3
Grouping ­ grouping similar data together to make it easier to manipulate
Eg. The group 10-19 contains all the data between 9.5 and 19.5
Ahistogramshows the frequency through its area
frequency
f requency density = width of interval
The frequency densityis shown on the vertical axis
f requency = width of interval ×frequency density
When values are ordered highest to lowest:
Median ­ middle value, can be used as the `average'
o If there are two values in the centre, the median is halfway between the two
Range ­ difference between highest value and lowest value ­ affected by extreme values
at upper and lower ends, which distort the entire picture
Lower quartile ­ Q1,
has 1
4 of the values less than or equal to it, so can be found halfway
between n n
4 th and ( 4 + 1) th value
Upper quartile­ Q , has 3 of the values less than or equal to it, so can be found halfway
3 4
between 3n th and (34n + 1) th value
4
o When finding quartiles, always round up
The median is Q 2
Interquartile range(IQR) is Q3 - Q1 and
tells us the spread of the `middle half' of the data
o This excludes extreme values and is a better measure of spread
The quartiles can be show using a box plot

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Outliers ­ an exceptionally high or low value
Tukey's rule ­ 1.5 × IQR beyond the upper or lower quartile is defined as an outlier
x < Q1 - 1.5(IQR) or x > Q3 + 1.…read more

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