2.2 Histograms • Relative Frequency Histograms • Interpreting Shape • Common Distribution Shapes • Normal Quantile Plots

What is the Relative Frequency formula?

Frequency in category / total frequency x 100

(Add up all frequencies/values)

**sum must =100

Define Histogram and what each axis represents

Histogram: bar graph of frequency distribution

Horizontal axis: class boundaries

Vertical axis: shows frequencies. Bars are touching each other since underlying data are continuous

What does a Relative Frequency Histogram show that a standard Histogram does not? Will it change the shape of the graph? What will it change?

RFH vertical axis shows “relative frequencies” (proportions or %’s) instead of raw counts. This will never change the shape of the graph, it will only change the vertical scale.

What 4 things does a Histogram Describe?

Center, Spread, Shape, and Outliers

What does Center mean in a Histogram

Typical value

What does Spread mean in a histogram?

How much data varies

What are the 4 shapes in a Histogram? (S.U.B.S.)

Symmetric, Uniform, Skewed, Bimodal

Describe a Normal shaped Histogram

Symmetric, bell shaped, even taper, single peak at center

Describe a Uniform shaped Histogram

All classes have roughly same height

Describe a Skewed shaped Histogram (direction and name)

Skewed Left: left tail and bunched right

Skewed Right: right tail and bunched left

Describe a Bimodal shaped Histogram

Two distinct peaks, suggesting two subgroups within the data

Define Normal Quantile Plots and what they represent

Straight Line Pattern → approximately normal

Curves/Bends → departure from normality

(J shape is skewed, S shape is light tailed/not normal)

Don’t forget about possible outliers - points shooting far off the line