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In general, the Quantile Functions (sometimes referred to
as Inverse Density Functions or Percent Point Functions) return the
Value X at which P(X) = [specified cumulative probability], given that particular
distribution.

- IDF_Beta: This
function takes the specified probability and returns the value X, such
that P(X) = P-value, given the Beta distribution with the two
specified Shape parameters. Because the formula for this function does
not exist in a closed form, it must be computed numerically. This
script arrives at the X-value through an iterative process, repeatedly
testing X-values with the CDF_Beta function until it arrives at P
value that is within 1x10-12 units from the specified
P-value (this usually takes between 30-60 iterations).
a) Parameters:
- P-value: Number (0 >= p
>= 1)
- Shape1: Number > 0
- Shape2: Number > 0
b) Usages:
- From "Probability Distribution Calculator",
select "Quantile (IDF)" and Beta distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Beta”, {P-value, Shape1, Shape2}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Beta”, {P-value, Shape1,
Shape2}})
- (Avenue): theProb = av.Run("Jennessent.IDF_Beta",
{P-value, Shape1, Shape2})
c) Function: |
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- IDF_Binomial:
This function takes the specified probability and returns the value X
such that the Probability of getting (X – 1) successes <= the Specified
Probability. This function takes an iterative approach to finding the
correct X value, repeatedly trying different values of X until it
reaches the correct one. This iterative process rarely takes more than
25 repetitions.
a) Parameters:
- P-value: Number (0 >= p >= 1)
- # Trials: Integer >= 2, # Successes
- Probability of Success: Number (0 >= p >= 1)
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Binomial distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Binomial”, {P-value, #Trials, Probability of Success}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Binomial”, {P-value, #Trials,
Probability of Success}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_Binomial", {P-value, #Trials, Probability of
Success})
c) Function: |
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IDF_Cauchy:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the Cauchy distribution with the
specified location and scale parameters. The Standardized Cauchy
distribution has Location = 0 and Scale = 1.a)
Parameters:
- P-value: Number (0 >= p >= 1)
- Location: Number
- Scale: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Cauchy distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Cauchy”, {P-value, Location, Scale}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Cauchy”, {P-value, Location,
Scale}})
- (Avenue): theProb = av.Run("Jennessent.IDF_Cauchy",
{P-value, Location, Scale})
c) Function: |
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IDF_ChiSquare:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the Chi-Square distribution with the
specified Degrees of Freedom. Because the formula for this function does
not exist in a closed form, it must be computed numerically. This script
arrives at the X-value through an iterative process, repeatedly testing
X-values with the CDF_ChiSquare function until it arrives at P value
that is within 1x10 -12 units from the specified P-value (this usually
takes between 30-60 iterations). The Chi-Square distribution results
when v (where v = Degrees of Freedom) independent variables with
standard normal distributions are squared and summed (Croarkin & Tobias,
Date unknown).a) Parameters:
- P-value: Number (0 >= p >= 1)
- Degrees of Freedom: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Chi Square distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_ChiSquare”, {P-value, DF}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_ChiSquare”, {P-value, DF}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_ChiSquare", {P-value, DF})
c) Function: |
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IDF_Exp: This
function takes the specified probability and returns the value X, such
that P(X) = P-value, given the Exponential distribution with the
specified mean. This script uses the 1-parameter version of the equation
(i.e. assuming Location = 0). The Standard Exponential Distribution is
that which has Mean = 1.
a) Parameters:
- P-value: Number (0 >= p >= 1)
- Mean: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Exponential distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Exp”, {P-value, Mean}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Exp”, {P-value, Mean}})
- (Avenue): theProb = av.Run("Jennessent.IDF_Exp",
{P-value, Mean})
c) Function: |
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IDF_F: This function
takes the specified probability and returns the value X, such that P(X)
= P-value, given the F distribution with the specified Degrees of
Freedom. Because the formula for this function does not exist in a
closed form, it must be computed numerically. This script arrives at the
X-value through an iterative process, repeatedly testing X-values with
the CDF_F function until it arrives at P value that is within 1x10-12
units from the specified P-value (this usually takes between 30-60
iterations). The F distribution is the ratio of two Chi Square
distributions with ratios v1 and v2 respectively.
a) Parameters:
- P-value: Number (0 >= p >= 1)
- 1st Degrees of Freedom: Number > 1
- 2nd Degrees of Freedom: Number > 1
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and F distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_F”, {P-value, DF1, DF2}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_F”, {P-value, DF1, DF2}})
- (Avenue): theProb = av.Run("Jennessent.IDF_F",
{P-value, DF1, DF2})
c) Function: |
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IDF_Logistic:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the Logistic distribution with the
specified mean and scale parameters.a)
Parameters:
- P-value: Number (0 >= p >= 1)
- Mean: Number
- Scale: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Logistic distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Logistic”, {P-value, Mean, Scale}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Logistic”, {P-value, Mean,
Scale}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_Logistic", {P-value, Mean, Scale})
c) Function: |
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IDF_LogNormal:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the LogNormal distribution with the
specified mean and scale parameters. Because the formula for this
function does not exist in a closed form, it must be computed
numerically. This script arrives at the X-value through an iterative
process, repeatedly testing X-values with the CDF_LogNormal function
until it arrives at P value that is within 1x10-12 units from
the specified P-value (this usually takes between 30-60 iterations). A
LogNormal distribution occurs when natural logarithms of variable X are
normally distributed. The Standard LogNormal Distribution is that with
Mean = 0 and Scale = 1. The 2-Parameter LogNormal Distribution is that
with Mean = 0.a) Parameters:
- P-value: Number (0 >= p >= 1)
- Mean: Number > 0
- Scale: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and LogNormal distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_LogNormal, {P-value, Mean, Scale}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_LogNormal, {P-value, Mean,
Scale}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_LogNormal", {P-value, Mean, Scale})
c) Function: |
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IDF_Normal:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the Normal distribution with the
specified mean and standard deviation. Because the formula for this
function does not exist in a closed form, it must be computed
numerically. This script arrives at the X-value through an iterative
process, repeatedly testing X-values with the CDF_Normal_Simpsons
function until it arrives at P value that is within 1x10-12
units from the specified P-value (this usually takes between 30-60
iterations). Furthermore, there is no closed formula for calculating the
Normal cumulative distribution function, so this script uses the
Simpson’s approximation method (Stewart 1998, p. 421-424) to calculate a
highly accurate estimate (accuracy to > 12 decimal places). The Standard
Normal Distribution is that with Mean = 0 and Standard Deviation = 1.
a) Parameters:
- P-value: Number (0 >= p >= 1)
- Mean: Number
- Standard Deviation: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Normal distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Normal_Simpsons, {P-value, Mean, St. Dev.}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Normal_Simpsons, {P-value,
Mean, St. Dev.}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_Normal_Simpsons", {P-value, Mean, St. Dev.})
c) Function: |
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IDF_Poisson: This
function takes the specified probability and returns the value X such
that the Probability of getting (X – 1) events <= the Specified
Probability. This function takes an iterative approach to finding the
correct X value, repeatedly trying different values of X until it
reaches the correct one.
a) Parameters:
- P-value: Number (0 >= p >= 1)
- Mean: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Poisson distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Poisson, {#P-value, Mean}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Poisson, {P-value, Mean}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_Poisson", {P-value, Mean})
c) Function: |
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IDF_StudentsT:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the Student’s T distribution with the
specified Degrees of Freedom. Because the formula for this function does
not exist in a closed form, it must be computed numerically. This script
arrives at the X-value through an iterative process, repeatedly testing
X-values with the CDF_StudentsT function until it arrives at P value
that is within 1x10-12 units from the specified P-value (this
usually takes between 30-60 iterations). A Student’s T distribution with
1df is a Cauchy Distribution, and it approaches a Normal distribution
when DF>30. Various sources recommend using the Normal distribution if
DF>100.a) Parameters:
- P-value: Number (0 >= p >= 1)
- Degrees of Freedom: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Student’s T distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_StudentsT, {P-value, DF}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_StudentsT, {P-value, DF}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_StudentsT", {P-value, DF})
c) Function: The IDF_StudentsT T Function is dependent
on whether the test value is positive or negative:
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IDF_Weibull:
This function takes the specified probability and returns the value X,
such that P(X) = P-value, given the Weibull distribution with the
specified Location, Scale and Shape parameters. The Standardized Weibull
Distribution is that with Location = 0 and Scale = 1. The 2-Parameter
Weibull Distribution is that with Location = 0.
a) Parameters:
- P-value: Number (0 >= p >= 1)
- Location: Number
- Scale: Number > 0
- Shape: Number > 0
b) Usages:
- From "Probability Distribution Calculator", select
"Quantile (IDF)" and Weibull distribution.
- (Avenue): theProb = av.Run("Jennessent.DistFunc”,
{“IDF_Weibull, {P-value, Location, Scale, Number}})
- (Avenue): theProb =
av.Run("Jennessent.TableDistFunc”, {“IDF_Weibull, {P-value, Location,
Scale, Number}})
- (Avenue): theProb =
av.Run("Jennessent.IDF_Weibull", {P-value, Location, Scale, Number})
c) Function: |
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Back to
Statistics/Distributions | Summary Statistics |
Probability
Calculators | References
Calculating
Summary Statistics with Avenue
Discussion of Distribution Functions:
Probability Density Functions | Cumulative Distribution Functions |
Quantile Functions
Download
Statistics Extension Manual
(Adobe PDF, version 5)

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