# STAT 101 Lecture Notes - Lecture 3: Normal Distribution, Standard Deviation, Statistical Inference

## Document Summary

Always plot your data: make a graph, usually a histogram, or a stemplot. Look for the overall pattern (shape, center, variability) and for striking deviations such as outliers. Calculate a numerical summary to briefly describe center and variability. Sometimes the overall pattern of a large number of observations is so regular that we can describe it by a smooth curve. Total area under curve equals one (or 100%) Area under curve between two values = proportion of population excepted in the interval. Both are used to describe center of density curve. Mean: point at which curve would balance if made of solid material. Median: point at which the area of the density curve is cut in half. Right: median < mean (longer tail, further the mean from median) In sum: where the tail"s direction, where"s mean. All normal curves have the same overall shape: symmetric, one central peaked, bell-shaped, mean=median.