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Appendix C Formula Functions Reference 475
Probability Functions
standard gamma distribution is less than or equal to the specified x. The Gamma Distribution function
is the inverse of Gamma Quantile function.
Gamma Quantile
Accepts a probability argument p, and returns the p th quantile from the standard gamma distribution
with the shape parameter you specify. The Gamma Quantile function is the inverse of the Gamma
Distribution function.
Figure C.11 Overlay Plot of Gamma Density with Shape Parameter 1, 3, and 5
Shape=1
Shape=3
Shape=5
C Formula Functions Reference
Normal Density
Accepts a quantile argument from the range of values for the standard normal distribution. It returns
the value of the standard normal probability density function (pdf) for the argument. For example, you
can create a column of quantile values (x) with the formula count(-3, 3, nrow()) and a second column
computed as Normal Density(X) to generate density values. Then select Graph > Overlay to plot the
normal density by x. Figure C.12 shows an overlay plot of normal density curves with various means
and standard deviations.
Normal Distribution
Accepts a quantile argument from the range of values for the standard normal distribution with mean 0
and standard deviation 1. It returns the probability that an observation from the standard normal
distribution is less than or equal to the specified quantile. For example, the expression Normal
Distribution(1.96) returns 0.975, the probability that an observation from the standard normal
distribution is less than or equal to the 1.96 th quantile. Also, you can specify mean and standard
deviation parameters to obtain probabilities from nonstandard normal distributions. The Normal
Distribution function is the inverse of the Normal Quantile function.
Normal Quantile (Probit)
Accepts a probability argument p, and returns the p th quantile from the standard normal distribution.
For example, the expression Normal Quantile(0.975) returns the 97.5% quantile from the standard
normal distribution, which evaluates as 1.96. Also, you can specify parameter values for the mean and
standard deviation to obtain quantiles from nonstandard normal distributions. The Normal Quantile
function is the inverse of the Normal Distribution function.