:orphan:
.. _ahelp_cdf:
***
cdf
***
.. contents:: :local:

.. codeblock:: none
Usage 1: cdf [v] t2p statname t params
Usage 2: cdf [v] p2t statname p params
Usage 3: cdf [v] t2z statname t params
This program does various conversions using the cumulative distribution
function (cdf) of certain canonical probability functions. The optional
'v' indicates to be verbose  this is for debugging purposes, mostly.
Use this option if you get results you don't understand!
Usage 1: Converts a statistic 't' to a tail probability.
Usage 2: Converts a tail probability 'p' to a statistic.
Usage 3: Converts a statistic 't' to a N(0,1) value (or zscore)
that has the same tail probability.
The parameter 'statname' refers to the type of distribution to be used.
The numbers in the params list are the auxiliary parameters for the
particular distribution. The following table shows the available
distribution functions and their parameters:
statname Description PARAMETERS
  
fico Cor SAMPLES FITPARAMETERS ORTPARAMETERS
fitt Ttest DEGREESofFREEDOM
fift Ftest NUMERATOR and DENOMINATOR DEGREESofFREEDOM
fizt Ztest N/A
fict ChiSq DEGREESofFREEDOM
fibt Beta A (numerator) and B (denominator)
fibn Binom NUMBERofTRIALS and PROBABILITYperTRIAL
figt Gamma SHAPE and SCALE
fipt Poisson MEAN
EXAMPLES:
Goal: find pvalue for tstatistic of 5.5 with 30 degrees of freedom
COMMAND: cdf t2p fitt 5.5 30
OUTPUT: p = 5.67857e06
Goal: find F(8,200) threshold that gives a pvalue of 0.001
COMMAND: cdf p2t fift 0.001 8 200
OUTPUT: t = 3.4343
The same functionality is also available in 3dcalc, 1deval, and
ccalc, using functions such as 'fift_t2p(t,a,b)'. In particular,
if you are scripting, ccalc is probably better to use than cdf,
since the output of
ccalc expr 'fitt_t2p(3,20)'
is the string '0.007076', while the output of
cdf t2p fitt 3 20
is the string 'p = 0.0070759'.