EC255 Chapter 3: Chapter 3 - Descriptive Statistics
Chapter 3: Descriptive Statistics
Numerical Data Properties
Measures of Central Tendency – Ungrouped Data
- Provide information about the center or middle part of a group of numbers
- Provide location information
- Common measures:
o Mode
o Median
o Mean
Mode
- The value that occurs most frequently
- Not effected by extreme values
- Could be no mode / could have several modes
Median
- Middle value in an ordered array of numbers
- Applicable for ordinal, interval and ratio data
- Not applicable for nominal data
- Not affected by extreme values
Mean
- Most common measure of central tendency
- = sum of values divided by the number of values
- affected by extreme values (outliers)
- not applicable for nominal/ordinal data
Some Notation
- Number of observations in population, N
- Number of observations in sample, n
- Mean for a population =
- Mean for a sample =
Measures of Variability – Ungrouped Data
- Used to indicate how much are the observations spread out
around the mean
- Common measures
o Range
o Mean absolute deviation
o Variance
o Standard deviation
o Coefficient of variation
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