Density Curves

A density curve is a curve that gives a rough description of a distribution. The curve is smooth, so any small irregularities in the data are ignored.



Density curves are always drawn above the horizontal axis on a graph.
The area under a density curve (between the curve and the horizontal axis) is always defined as 1 unit.
The area under a density curve between two values is the proportion of observations in the data set that fall between those two values.

When a distributions density curve is similar enough to a density curve with known properties, we can use those properties to obtain information about the distribution.

Because a density curve is an idealised description of a distribution, rather than a perfectly accurate one, its mean and standard deviation are slightly different from those values of the actual data. Because they are different, they are given different symbols. The mean of a density curve has the symbol µ, while the standard deviation has the symbol σ.

Continue to next section: Normal Curves