Chapter 8 – Bell-Shaped Curves and Other Shapes
The most common type of picture for a population is a smooth frequency curve. The vertical scale is
labeled “height of the curve”. The area under the curve is equal to 1. Normal distribution is a
measurement that follows a certain shape. It is also called a bell-shaped curve or a Gaussian curve. Not
all frequency curves are bell-shaped. They are helpful for determining what proportion of the population
falls into a certain range. To find the proportion from a stemplot you count the leaves in the range and
divide by the total. In a histogram we would add the heights of the bars and divide by the total.
Nature has many normal curves. Many academic tests have normal curves as well. This is not surprising
because most people are somewhere near average and very few are at the extremes. Sometimes people
grade on a bell curve. This makes more people normal and a few at the extremes.
Percentile is the position in a pop