STAT 111 Lecture Notes - Lecture 5: Standard Deviation, Percentile, Interquartile Range

• School: University of Vermont
• Department: Statistics
• Course: STAT 111
• Professor: Jacob William Martin

Document Summary

The standard deviation for a quantitative variable measure the spread of the data. The standard deviation gives a rough estimate of the typical distance of a data values from the mean. The larger the standard deviation, the more variability there is in the data and the more spread out the data are. If a distribution of data is approximately bell-shaped, about 95% of the data should fall within two standard deviations of the mean. For a population, 95% of the data will be between -2 standard deviations to +2 standard deviations. A z-score puts values on a common scale. Values farther from 0 are more extreme. A z-score is the number of standard deviations a value falls from the mean. The pth percentile is the value which is greater than p% of the data. Quartiles: q1 = median of the values below m. q3 = median of the values above.