SDA: Distributions/Skew

Question 1

What is normal distribution?

Answer 1

Symmetrical dispersion

Mode=Median=Mean

Question 2

What is bimodal distribution?

Answer 2

Data with 2 Modes

NB: must draw histograms to know if data is bimodal as may be hidden in data tables

Question 3

Positive skew

Answer 3

Mean>Median>Mode

Highest point furthest left

Question 4

Negative skew

Answer 4

Mode>Median>Mean

Highest point furthest right

Question 5

Inter-quartile range

Answer 5

Upper quartile minus lower quartile

i.e. Q3-Q1

Question 6

What is the ‘fence’ calculation?

Answer 6

1.5xdQ

Any values that are 1.5 times dQ above or below Q1 and Q3 are outliers

Question 7

What are the three ways to measure spread?

Answer 7

Variance
Standard Deviation
Coefficent of variation

Question 8

What is the notation for the inter-quartile range?

Answer 8

dQ

Question 9

Which measurement of spread is preferred? Variance or Standard Deviation?

Answer 9

Standard deviation because it’s measured in data units rather than data units squared as with variance

Question 10

What is the advantage of the Coefficient of Variation measurement of spread?

Answer 10

Allows comparisons of spread for different variables