# Statistics AS Flashcards

Sum of the data notation

Σx

Mean of the data notation

x bar

X bar =

Σx / n

Q1 =

n/4

Q2 =

n/2

n3 =

3n /4

IQR =

Q3 - Q1

X bar = (from frequency table)

Σx2 / Σf

Median from UNGROUPED data set

n + 1 / 2

Median from GROUPED data

n / 2

Linear interpolation =

x - lower bound / group width = percentile - lower bound / group width

σ^2 = (variance)

Σx^2/n - (Σx/n)^2

σ = (standard deviation)

Sqrt(Σx^2/n - (Σx/n)^2)

σ = (from coding)

Sqrt (Sxx summary stats / n)

σ^2 = (from frequency table)

Σxf ^2/Σf - (Σfx/Σf)^2

σ =(from frequency table)

Sqrt(Σxf ^2/Σf - (Σfx/Σf)^2)

Mean of y from code y = ax + b

a (x bar) + b

a times mean of x. Add b

Standard deviation of y from code y = ax + b

σy = a(σx)

a times standard deviation of x

Outlier definition

out of 1.5x IQR from Q1 or Q3

Or 2 standard deviations from mean

Frequency =

frequency density x class width x k

Where k is constant

Frequency = (from histogram)

k x area

Where k is a constant

How to draw a frequency polygon

Join up midpoints

Define cleaning the data

Removing incorrect data values (anomalies)