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Unformatted text preview: 1 CHAPTER 4: DESCRIPTIVE STATISTICS Stats & Prob. for Bus. Mgmt (Stat1100) Jochem Descriptive Statistics b Overview b 1. What is Descriptive Statistics? s Sample versus Population b 2. Measures of Central Location 2 b 3. Measures of Dispersion b 4. Measures of Relative Standing b 5. Measures of Linear Relationships b 6. Misc s 5-Number Summary s Outlier Rule Descriptive Statistics b 1. What is Descriptive Statistics? b Question: s Suppose you have some data set and you would like to tell someone about it without having to show him each 3 single data point. What do you do? s (Or, the data set is simply so large that you get a headache from looking at thousands of values.) b Answer: s You may try to come up with some summary statistics that somehow describe the data set. Simply put, all that is descriptive statistics. Descriptive Statistics b 1. What is Descriptive Statistics? b Examples: s Measures of Central Location s Mean (arithmetic, geometric), Mode, Median 4 s Measures of Dispersion (or Spread, Variability) s Range, Interquartile Range, Mean Absolute Deviation (MAD) s Variance, Standard Deviation s Coefficient of Variation s Measures of Relative Standing s Percentiles (Quartiles, Quintiles, Deciles) s z-Score s Measures of Linear Relationships s Correlation, Covariance These are the most commonly used ones. There is nothing like a “right” vs. “wrong” measure. You can also come up with your own new measures if you like to that seem better to you! Descriptive Statistics b 1. What is Descriptive Statistics? b Recall: Population versus Sample s The population of a study is the group of all items of interest in that study. 5 s A sample is a subset of the population that is studied. s Note that the mean of the sample of course differs from the mean of the population – in fact, every time we take a sample, its mean will slightly be different. B We need to differentiate between the sample mean and population mean. “Sampling Process” (next chapter) Descriptive Statistics b 1. What is Descriptive Statistics? b Recall: Population versus Sample s To differentiate between a population parameter and a sample statistic, we use Greek letters vs. Latin-based letters. 6 s Example: (pronounced x-bar) refers to a sample mean (pronounced mu) refers to the population mean Why Greek? No one could tell me so far why. Here is my personal mental bridge for remembering that Greek letters are population parameters: the population mean is unknown to us so it is somewhat “mystique” -- as anything mystique is “all Greek to us”, we use Greek letters for unknown mystique population statistics. Descriptive Statistics b 1. What is Descriptive Statistics? s Don’t get confused when seeing Greek letters. It’s just a fancy way of referring to some (typically nknown) population parameter....
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This note was uploaded on 03/26/2012 for the course STAT 1100 taught by Professor Chiappetta during the Spring '08 term at Pittsburgh.
- Spring '08