Measures Of Spread Flashcards
What is the range of data
How far the data spreads
How do you find the range of data
Find the difference between the highest and the lowest values
What is q1 called
The lower quartile
What is q2 called
The median
What is q3 called
The upper quartile
What percentage is q1
25%
What percentage is q2
50%
What percentage is q3
75%
Calculation for q1
(N+1)/4
What is the calculation for q2
2(n+1)/4
What is the calculation for q3
3(n+1)/4
What do you do with the values worked out in the quartile equations
Find that value on the list of the numbers
What do percentiles p1 to p99 do
Divide the data into 100 equal groups
Formula to work out percentiles
P1 Position number =(n+1)/ 100. P2 position number= 2(n+1)/100. Etc
What should you do if your percentile doesn’t fall on a whole number
Take the 2 numbers it lies between and find there mean
What is the interquartile range
The difference between the upper and lower quartile
Icr formula
Q3- Q1
How to find the Inter percentile range
Find the difference between the 2 percentiles
What do deciles divide the data into
Ten equal groups
How to find deciles
D9 = 9(n+1)/10
What is the Inter decile range
The difference between the first 9 deciles
D9 -D1
What does having a large interquartile/percentile/decile range mean
That the data is spread out in their region
It’s more varied and less consistent
What does having a small interquartile/percentile/decile range mean
That the data is more consistent and less varied
What does the interquartile range tell you
The range of the middle 50% of the data where most activity is going on and is unaffected by outliers
What is a disadvantage of the icr
Omits 50% of the data
Advantages of using small percentile ranges
Let’s you see what is going on in smaller areas
Why does the Inter decile range give a more realist idea to the spread of data than the range or interquartile range
It give the middle 80% and ignores any outliers
