Lesson # 8

Front 1

Range v Interquartile Range (IQR)

Back 1

Range: Max-Min
IQR: Q3-Q1

Front 2

Advantages of IQR and Range

Back 2

1.Simple to compute
2. IQR not sensitive to outliers

Front 3

Disadvantages of Range and IQR

Back 3

1.Don't involve actual values of all data points
2.not commonly used
3.have complex theoretical properties
4. Range is sensitive to outliers
5. As n increases range becomes less precise

Front 4

Computing Std. Dev

Back 4

1. Measure center as reference point(usu.mean over median)
2. Compute distances from data points to a reference point(x-x bar or mean)
3.Select a representative deviation

Front 5

Further on std.dev

Back 5

1. Average of deviation are always zero.(see last mem card)
2.Deviations to the left of mean are negaative
3. See formula for Std.Dev

Front 6

Steps for calculating std.dev by hand

Back 6

find x minus mean for each value and square all values.add them up and divide by n minus 1.take square root of ans and u hav it!

Front 7

Properties of STD.DEV

Back 7

1.Measures spread around mean (use 's' only when mean is the appropriate center)
2. it is either zero or positive. (s=0 data dont vary)
3.Unit is same as that of observations
4.inflated by outliers

Front 8

Diff b/w std.dev and variance

Back 8

Variance: s2:this is average squared deviation from mean.
Std.Dev: s: square root of variance

Front 9

Population vs Sample (notation for std.dev)

Back 9

Population:
sigma, meu, N
Sample:
S,x bar,n-1

Front 10

Why divide by n-1?

Back 10

1. establish important theoretical properties for inference
2.to make sample variance (S2)an unbiased estimate of population variance(sigma2)

Front 11

Advantages and Disadvantages of Std.Dev

Back 11

ADVANTAGES:
1.Commonly used
2.Deiations from every point unlike range and IQR
3.Good theoretical properties
DISADVANTAGES
Inflated by outliers/skewness

Front 12

Median & IQR (Vs) Mean & Std.Dev

Back 12

Median & IQR for skewed dis/outliers. (Mean and std.dev affected by outliers/skewed
Symmetrical Dist use mean and std.dev

Front 13

Rule of thumb

Back 13

Std.Dev is usually less than one fourth of the range