ISDS 361B Ch. 4

• Mean
• Median
• Mode

It is the average.

• Central location. gives you the middle where 50% of the numbers lie on each side.
• *When there is an even # of observations, the median is determined by averaging the 2 observations in the middle.

the observation with the greatest frequency

• In small samples not a good measure to use
• it may not be unique

Data Anaylsis --> Descriptive Statistics (then input the range of numbers) --> Summary statistics.

Mean is used most often, but median could be better because it is not sensitive to extreme values.

• Interval data
• u want to describe a single set of data

• Interval or Ordinal data (w/extreme observations)
• Describe a single set of data

Ordinal data - categorized with meaning

Largest observation - Smallest observation


pg. 106

• Range
• Variance
• Standard Deviation
• Coefficient of Variation

No, cuz it only gives us a rough idea of the variation in the data. Comparing to another set of data it could tell us if the 1st set of data has more variation than the 2nd set.

you calc the standard deviation. Units associated with SD is the unit of the original data set.


pg. 110

• Empirical Rule - Bell Shape
• Chebysheff's Theorem - all shapes

• 68% fall in between 1 SD, so 18% and 2%
• 95% fall in between 2 SD, so 26% and -6%
• 99.7% fall in between 3 SD

• provides lower bounds
• 75% lie between 2 SD
• 88.9% lie between 3 SD

Indicates whether the SD (variation) is large or small compared to the number of observations.

SD / by their mean

• At least 75% of the numbers lie between
• At least 88.9% of the numbers lie between