normal+curve

Normal curve is a theoretical model. It is kind of line chart that is unimodal. Unimodal means that mean = median = mode. Normal curve is bell shaped and its tails extends in both directions endlessly.

In combination with the mean and standard deviation, the normal curve can be used to construct precise descriptive statements about empirical distributions. Normal curve is shaped in a way that on any given point the distance from it to the mean (when measured in standard deviations) will cut off exactly the same proportion of the total area.

There are two kinds of Normal curves: Actual Normal curve, which represents the distribution of actual data and Standard Normal curve, where the sample mean and standard deviation are transformed into standard values with mean as zero and standard deviation of 1. Therefore the area under the curve shows probability of being between various values of standard deviation.

Source: Healey, Joseph, F. 2009. Statistics: A tool for Social Research. 8.edition. Belmont: Wadsworth Cengage Learning. pp.115-116.