Figure 25
where is calledthe probabilitydensityfunction (pdf).One of the mostusefulprobabilitydensity
functionsis thenormalcurveor theGaussiancurve(and sometimesthebell curve) (Figure26). This
functionenablesus to describean entirepopulationbasedon statisticalmeasurementstakenfrom a small
sampleof the population.The only measurementsneededare the mean( ) and the standarddeviation
( ). Oncethosetwo numbersare known,we can easilyfind the normalcurveby usingthe followingformula.
Figure 26
The NormalProbabilityDensityFunction
The Gaussiancurvefor a populationwith meanμ and standarddeviation is givenby