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Probability Density Function Calculator

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Explore the probability of a continuous random variable using a free probability density function calculator. Let’s dive deeper to understand the concept and see how this tool can save time and provide accurate results.

What Is a Probability Density Function?

In statistics:

“A probability density function (PDF) is a function that describes the likelihood of a continuous random variable taking on a specific range of values.”

It is also known as a probability distribution function.

Note: The integral of a PDF over its entire range is always equal to 1.

Probability Density Curve:

Probability density curve example

This curve shows how probabilities are distributed. A free PDF calculator allows you to compute values quickly and visualize the curve easily.

Probability Density Function Formulas:

Beta Distribution:

The beta distribution is defined by two shape parameters:

$$ B(x, y) = \int t^{x-1} (1-t)^{y-1} dt $$
$$ f(x; a, b) = \frac{1}{B(a, b)} x^{a-1} (1-x)^{b-1} $$

a, b: shape parameters
B: beta function

Chi-Square Distribution:

Used to test relationships between categorical variables:

$$ f(x; k) = \frac{1}{2^{k/2} \Gamma(k/2)} x^{k/2 - 1} e^{-x/2} $$

k: degrees of freedom
Γ: gamma function

F-Distribution:

Used to compare variances of two datasets:

$$ f(x; d_1, d_2) = \frac{\sqrt{\frac{(d_1 x)^{d_1} d_2^{d_2}}{(d_1 x + d_2)^{d_1 + d_2}}}}{x B\left(\frac{d_1}{2}, \frac{d_2}{2}\right)} $$

d1, d2: degrees of freedom
B: beta function

Continuous Uniform Distribution:

Represents equal probability across a range:

$$ f(x) = \begin{cases} \frac{1}{b-a}, & a \le x \le b \\ 0, & \text{otherwise} \end{cases} $$

a: lower bound
b: upper bound
x: value to evaluate

T-Distribution:

Used when the population variance is unknown:

$$ f(t) = \frac{\Gamma\left(\frac{v+1}{2}\right)}{\sqrt{v \pi} \, \Gamma\left(\frac{v}{2}\right)} \left(1 + \frac{t^2}{v}\right)^{-\frac{v+1}{2}} $$

v: degrees of freedom
Γ: gamma function

Standard Normal Distribution:

Special normal distribution with mean 0 and standard deviation 1:

$$ \phi(x) = \frac{1}{\sqrt{2\pi}} e^{-\frac{1}{2} x^2} $$

Normal Distribution:

For any mean and standard deviation:

$$ f(x) = \frac{1}{\sqrt{2\pi \sigma^2}} e^{-\frac{(x-\mu)^2}{2\sigma^2}} $$

μ: mean
σ: standard deviation

Example Calculation:

Find the PDF of a normal distribution where:

  • x = 24
  • μ = 3.3
  • σ = 2

Solution:

$$ f(x) = \frac{1}{\sqrt{2\pi \sigma^2}} e^{-\frac{(x-\mu)^2}{2\sigma^2}} $$

Substitute values:

$$ f(24) = \frac{1}{\sqrt{2*3.14*2^2}} e^{-\frac{(24-3.3)^2}{2*2^2}} $$ $$ f(24) \approx 1.093 \times 10^{-24} $$

How the Probability Density Function Calculator Works

  • Select the distribution type from the dropdown.
  • Enter the required parameters.
  • Click Calculate to get the PDF value.

FAQs

What is the difference between PDF and CDF?

Cumulative Distribution Function (CDF) Probability Density Function (PDF)
Probability that a variable ≤ x Likelihood of a variable being exactly x

What is k in probability?

In probability, k represents the number of successes in n trials (binomial coefficient). Learn more using our binomial distribution calculator.

Difference between probability and probability density?

Probability is the area under the PDF curve. Probability density is the likelihood at a specific point. Use our probability calculator for computations.

What is the NORMDIST function in Excel?

NORMDIST calculates normal distribution probabilities given mean and standard deviation.

What does 1.96 mean in statistics?

It represents the 97.5th percentile of a standard normal distribution. Check percentiles using our percentile calculator.

Conclusion

Probability distributions describe the likelihood of outcomes in a dataset. Using a PDF calculator helps quickly analyze distributions, variances, and probabilities for continuous data.

References

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