| Want to work with gamma probability | | | | |
| distributions? But a quick explanation is | | | | If you have been given a probability and want |
| order if you're not familiar with this | | | | to find x, you use the GAMMAINV |
| powerful statistical concept and technique. | | | | function,which has the following syntax: |
| Here's the situation: If a Poisson process | | | | |
| produces successes at a constant rate of m | | | | =GAMMAINV (probability, alpha, beta) |
| per unit of time, then the random variable x, | | | | |
| the elapsed time until the rth success, | | | | For example, if the probability equals .5, |
| follows the gamma distribution. | | | | alpha equals 8, and beta equals 9, you use |
| | | | the followingformula: |
| The gamma distribution is often used to | | | | |
| determine the amount of time it takes for the | | | | =GAMMAINV (.5,8,9) |
| rth person to arrive in a line. | | | | |
| | | | The function returns the value 69.02. |
| Using the GAMMADIST Function | | | | |
| | | | Using the GAMMALN Function |
| If you know x and want to find the | | | | |
| probability, you use the GAMMADIST function, | | | | You use the GAMMALN function to find the |
| whichhas the following syntax: | | | | natural logarithm of the gamma function, |
| | | | G(x). The GAMMALN function uses the following |
| =GAMMADIST(x, alpha, beta, cumulative) | | | | syntax: |
| | | | |
| For example, if x equals 25, alpha equals 8, | | | | =GAMMALN(x) |
| beta equals 9, and cumulatative is TRUE, | | | | |
| youuse the following formula: | | | | For example, if x equals 25, you use the |
| | | | following formula: |
| =GAMMADIST (25,8,9,TRUE) | | | | |
| | | | =GAMMALN(25) |
| The function returns the value 0.007774. | | | | |
| | | | The function returns the value 54.78. |
| Using the GAMMAINV Fucntion | | | | |