S- Central tendency, median, variance & standard deviation- ED Flashcards
How do you work out the mean (x̄)
Σx ÷ n
How do you work out mean in a frequency table?
Σfx ÷ Σx
How do you work out median & what do you do with it?
n÷2, If a decimal- round up, if whole use halfway between this item and another
How do you work out median in grouped data?
n÷2, no rounding- use linear interpolation
What is the formula when doing linear interpolation?
a/c = b/d
What are Q1,Q2 & Q3?
Q1= Lower quartile
Q2= Median
Q3= Upper quartile
How do you show a percentile?
Pn e.g. 11th percentile = P11
Why is the interquartile range good?
Excludes outliers & extreme values
In Listed data, how do you work out the LQ & UQ?
LQ= n÷4
UQ= n÷4 x 3
If a decimal, round up
If whole, halfway between this & one after
In Grouped data how do you work out LQ & UQ?
LQ= n÷4
UQ= n÷4 x 3
No rounding- linear interpolation
What is variance?
A measure of spread that takes all values into account- the average squared distance from the mean
What is the formula for variance?
σ2= Σx squared ÷ n - x̅ squared
What does Σ mean?
The sum of
What is the formula for standard deviation?
σ= √ variance
What is the formula for variance in a frequency table?
σ2= Σfx squared ÷ Σf - x̅ squared
