sdist

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 — sdist [2010/06/11 01:54] (current)jochen created 2010/06/11 01:54 jochen created 2010/06/11 01:54 jochen created Line 1: Line 1: + ====== sdist - statistical distribution functions ====== + ===== Motivation ===== + For many tasks in statistical hypothesis testing, it is necessary to find the ordinate value where the cumulative distibution function reaches a particular value (inverse of the CDF). These functions are available in Matlab'​s stats toolbox, but to allow users without this toolbox to use NeuroElf, freely available code has been edited and put into one compound function, ''​sdist''​. + + ===== Function reference ('help sdist'​) ===== + <​file> ​ sdist  - statistics distributions + + FORMAT: ​      d = sdist(type, variate, df1 [, df2 [, pin]]) + + Input fields: + + type        either of '​betacdf',​ '​betainv',​ '​betapdf',​ + '​fcdf',​ '​finv',​ '​fpdf',​ '​tcdf',​ '​tinv',​ '​tpdf'​ + variate ​    ​variate (or p-value) + df1, df2    d.f. (or other required parameter) + pin         ​logical flag, inverse from 0.9 to 0.1 logic + + Output fields: + + d           ​determined value of requested distribution function + ​ + + ===== Usage examples ===== + * find the value required to threshold a t-map with 25 degrees of freedom at p<0.005 (uncorr.):<​code matlab>​sdist('​tinv',​ 0.995, 25)​ + * find the value required to threshold an F-map with (3, 20) degrees of freedom at p<0.01 (uncorr.):<​code matlab>​sdist('​finv',​ 0.99, 3, 20)​ + * find out if a given t-statistic (3.314, df = 115) is enough to meet a specific alpha criterion (0.001):<​code matlab>​sdist('​tcdf',​ 3.314, 115) >= 0.999