# ECO-2100 Lecture Notes - Lecture 3: Skewness, Frequency Distribution, Unimodality

46 views2 pages

Eco 2100 Chapter Three notes

•A histogram is a graphical representation of a frequency distribution.

•The Y-axis of a histogram shows the frequency or percentage (relative frequency) of each bin

Shape:

Modal Class: a histogram bar that is higher than those on either side

Unimodal, bimodal, trimodal, multimodal

Modal classes may be artifacts of the way bin limits are chosen.!

Skewness: the direction of the longer tail of a histogram.

Left skewed - (negatively skewed) a longer left tail

Right skewed - (positively skewed) a longer right tail

Symmetric - both tail areas are the same

Two ways to determine the skewness of the distribution of all data values in a sample

One: plot a histogram

Two: compare the mean, median, and mode

Mode>Median>Mean - skewed left (Mode is largest)

Mean=Median=Mode - symmetric

Mode<Median<Mean - skewed right (Mean is largest)

Chapter Four Notes

Mean:

•The mean is the balancing point

•In Excel, use the function AVERAGE(Data)

Median:

•The median is the midpoint of a sorted sample data.

•If n (sample size) is odd, the median is the middle observation in a sorted data array.

•If n is even, the median is the average of the middle two observations in a sorted data array

•In Excel, use the function MEDIAN(Data)

•Median vs. Mean

•Median is very stable compared to mean

find more resources at oneclass.com

find more resources at oneclass.com