Statistic 101 Notes

1. Descriptive Stats:

* Descriptive statistics, meaning the use of statistical and graphic techniques to present information about the data set being studied

* The Mean: The mean is an intuitive measure of central tendency that is easy for most people to understand. However, the mean is not an appropriate summary measure for every data set because it is sensitive to extreme values, also known as outliers (discussed further later) and can also be misleading for skewed (nonsymmetrical) data. the median is often reported instead

* The Median: The median of a data set is the middle value when the values are ranked in ascending or descending order. If there are n values, the median is formally defined as the (n +1)/2th value. If there is an even number of values, the median is the average of the two middle values. The median is a better measure of central tendency than the mean for data that is asymmetrical or contains outliers. This is because the median is based on the ranks of data points rather than their actual values, and by definition, half of the data values in a distribution lie below the median and half above the median, without regard to the actual values in question. Therefore, it does not matter whether the data set contains some extremely large or small values because they will not affect the median more than less extreme values.

* The Mode: A third common measure of central tendency is the mode, which refers to the most frequently occurring value. The mode is most often useful in describing ordinal or categorical data. For instance

* Comparing the Mean, Median, Mode

* In a perfectly symmetrical distribution (such as the normal distribution, discussed in Chapter 3), the mean, median, and mode are identical. In an asymmetrical or skewed distribution, these three measures will differ

* A mean higher than a median is common for right-skewed data because the extreme higher values pull the mean up but do not have...