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Differences between revisions 22 and 23
 ⇤ ← Revision 22 as of 2008-02-13 12:35:59 → Size: 925 Editor: PeterWatson Comment: ← Revision 23 as of 2008-02-13 14:51:08 → ⇥ Size: 924 Editor: PeterWatson Comment: Deletions are marked like this. Additions are marked like this. Line 15: Line 15: \$\$A^text{-1/B}ln(2)^text{-1/B}\$\$ \$\$A^text{-1/B}ln(2)^text{1/B}\$\$

# How do I produce random variables which follow a negatively skewed distribution?

Most distributions such as the exponential and log-Normal distributions are positively skewed with the mode of the distribution occurring for lower values.

The Weibull distribution is negatively skewed and may be generated [http://www.taygeta.com/random/weibull.xml using random variables which are uniform on the interval (0,1).]

The below produces an open ended negatively skewed weibull distribution with parameters, 2 and 20. It has a median of

\$\$2text{-0.05}ln(2)text{0.05}\$\$ = 0.95.

which is of form

\$\$Atext{-1/B}ln(2)text{1/B}\$\$

where A and B are the two parameters of the Weibull distribution. (See [http://www.weibull.com/AccelTestWeb/weibull_distribution.htm here for formulae).]

```compute alpha=2.
compute beta=20.

compute rvw=((-1/alpha)*(ln(1-rv.uniform(0,1))))**(1/beta).
exe.```

None: FAQ/gamma (last edited 2013-03-08 10:17:36 by localhost)