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Legacy Tools › ArcView 3.x Extensions › Probability Density Functions

Probability Density Functions

In general, the Probability Density Functions return the probability that the Test Value = X, given that particular distribution.

Distributions
Beta Chi Square Logistic Poisson
Binomial Exponential LogNormal Student's T
Cauchy F Normal Weibull
  1. PDF_Beta: This function returns the probability that the Test Value = X, assuming a Beta distribution with the specified Shape parameters. This is the Standardized Beta function, where Location = 0 and Scale (upper bound) = 1. According to McLaughlin (2001), parameters Shape1 and Shape2 can be any positive value, but they rarely exceed 10. The function becomes nearly flat if the values get much larger than this.

    a) Parameters:

    1. Test Value: Number 
    2. Shape1: Number > 0
    3. Shape2: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Beta distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Beta”, {Test Value, Shape1, Shape2}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Beta”, {Test Value, Shape1, Shape2}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Beta", {Test Value, Shape1, Shape2})
       

c) Function:
  1. PDF_Binomial: The Binomial distribution is used when there are exactly two mutually exclusive outcomes of a trial. This function returns the probability of getting X successes out of N trials, given a probability of success = P.

    a) Parameters:

    1. # Successes: Integer >= 0
    2. # Trials: Integer >= 2, # Successes
    3. Probability of Success: Number (0 >= p >= 1)

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Binomial distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Binomial”, {#Success, #Trials, Probability of Success}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Binomial”, {#Success, #Trials, Probability of Success}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Binomial", {#Success, #Trials, Probability of Success})
       

c) Function:

 

  • PDF_Cauchy: This function returns the probability that the Test Value = X, assuming a Cauchy distribution with the specified Location and Scale parameters. The Standardized Cauchy distribution has Location = 0 and Scale = 1.

    a) Parameters:

    1. Test Value: Number
    2. Location: Number
    3. Scale: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Cauchy distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Cauchy”, {Test Value, Location, Scale}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Cauchy”, {Test Value, Location, Scale}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Cauchy", {Test Value, Location, Scale})
       

    • c) Function:

     

  • PDF_ChiSquare: This function returns the probability that the Test Value = X, assuming a Chi-Square distribution with the specified Degrees of Freedom. 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:

    1. Test Value: Number >= 0
    2. Degrees of Freedom: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Chi Square distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_ChiSquare”, {Test Value, DF}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_ChiSquare”, {Test Value, DF}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_ChiSquare", {Test Value, DF})
       

    • c) Function:

     

  • PDF_Exp: This function returns the probability that the Test Value = X, assuming an 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:

    1. Test Value: Number >= 0
    2. Mean: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Exponential distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Exp”, {Test Value, Mean}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Exp”, {Test Value, Mean}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Exp", {Test Value, Mean})
       

    • c) Function:

     

  • PDF_F: This function returns the probability that the Test Value = X, assuming an F distribution with the specified Degrees of Freedom. The F distribution is the ratio of two Chi Square distributions with ratios v1 and v2 respectively.

    a) Parameters:

    1. Test Value: Number >= 1
    2. 1st Degrees of Freedom: Number > 1
    3. 2nd Degrees of Freedom: Number > 1

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and F distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_F”, {Test Value, DF1, DF2}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_F”, {Test Value, DF1, DF2}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_F", {Test Value, DF1, DF2})
       

    • c) Function:

     

  • PDF_Logistic: This function returns the probability that the Test Value = X, assuming a Logistic distribution with the specified mean and scale.

    a) Parameters:

    1. Test Value: Number
    2. Mean: Number
    3. Scale: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Logistic distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Logistic”, {Test Value, Mean, Scale}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Logistic”, {Test Value, Mean, Scale}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Logistic", {Test Value, Mean, Scale})
       

    • c) Function:

     

  • PDF_LogNormal: This function returns the probability that the Test Value = X, assuming a LogNormal distribution with the specified mean and scale. 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:

    1. Test Value: Number >= 0
    2. Mean: Number > 0
    3. Scale: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and LogNormal distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_LogNormal, {Test Value, Mean, Scale}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_LogNormal, {Test Value, Mean, Scale}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_LogNormal", {Test Value, Mean, Scale})
       

    • c) Function:

     

  • PDF_Normal: This function returns the probability that the Test Value = X, assuming a Normal distribution with the specified mean and standard deviation. The Standard Normal Distribution is that with Mean = 0 and Standard Deviation = 1.

    a) Parameters:

    1. Test Value: Number
    2. Mean: Number
    3. Standard Deviation: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Normal distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Normal_Simpsons, {Test Value, Mean, St. Dev.}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Normal_Simpsons, {Test Value, Mean, St. Dev.}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Normal_Simpsons", {Test Value, Mean, St. Dev.})
       

    • c) Function:

     

  • PDF_Poisson: This function returns the probability that the specified Number of Events will be = X, assuming a Poisson distribution with the specified mean.

    a) Parameters:

    1. # Events: Integer >= 0
    2. Mean: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Poisson distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Poisson, {# Events, Mean}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Poisson, {# Events, Mean}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Poisson", {# Events, Mean})
       

    • c) Function:

     

  • PDF_StudentsT: This function returns the probability that the Test Value = X, assuming a Students T distribution with the specified Degrees of Freedom. 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:

    1. Test Value: Number
    2. Degrees of Freedom: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Student’s T distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_StudentsT, {Test Value, DF}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_StudentsT, {Test Value, DF}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_StudentsT", {Test Value, DF})

    c) Function: The PDF_StudentsT T Function is dependent on whether the test value is positive or negative:

    •  

  • PDF_Weibull: This function returns the probability that the Test Value = X, assuming a 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:

    1. Test Value: Number > Location
    2. Location: Number
    3. Scale: Number > 0
    4. Shape: Number > 0

    b) Usages:

    1. From "Probability Distribution Calculator", select "Probability (PDF)" and Weibull distribution.
    2. (Avenue): theProb = av.Run("Jennessent.DistFunc”, {“PDF_Weibull, {Test Value, Location, Scale, Number}})
    3. (Avenue): theProb = av.Run("Jennessent.TableDistFunc”, {“PDF_Weibull, {Test Value, Location, Scale, Number}})
    4. (Avenue): theProb = av.Run("Jennessent.PDF_Weibull", {Test Value, Location, Scale, Number})
       

    • c) Function:

    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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