Normal Distribution The normal distribution is the familiar bell-shaped curve, It is useful in simulation modeling as a continuous input distribution. However, it is not always the most appropriate distribution. It is symmetric, which can be a drawback when a skewed distribution is more realistic. Also, it allows negative values, which are not appropriate in many situations.
A tip-off that a normal distribution might be an appropriate candidate for an input variable is a statement such as, “We believe the most likely value of demand is 100, and the chances are about 95% that demand will be no more than 40 units on either of side of this most likely value.” Because a normally distributed value is within two standard deviations of its mean with probability 0.95, this statement translates easily to a mean of 100 and a standard deviation of 20. This does not imply that a normal distribution is the only candidate for the distribution of demand, but the statement suggests that the normal distribution is a good candidate.