function is_effect(dir)
% FORMAT is_effect(dir)
%
% Calculate p values for probability of any effect in an 
% F map for a given analysis (as defined by SPM files)
% using Worsley's average F test
%
% Matthew Brett 10/10/98 - copied from code by Tom Nichols

if nargin < 1
	dir = spm_get(-1, [], 'Select directory containing analysis');
end

load([dir '/SPM']);

fprintf('Loading SPMF... ')
load([dir '/SPMF']);
fprintf('Done.\n\n');

if length(SPMF)~= S
	error('Not all voxels were saved, cannot calculate p value')
end

% Volume, resels and smoothness 
%------------------------------------------------------------------------
D     = length(W);					% dimension of SPM
FWHM   = sqrt(8*log(2))*W.*V(([1:length(W)] + 3))';
RESELS= S*prod(V([1:D] + 3))/prod(FWHM);		% RESELS
d     = RESELS*(4*log(2)/pi)^(D/2);   		% effect. spatial df

% df
h = Fdf(1);	  % df for effects of interest
nu = Fdf(2);  % df due to error, whole model

% average F
mF = mean(SPMF);

% Global F-stat
%-----------------------------------------------------------
Fdf    = [d*h, d*nu-(d-1)*(4*h+2*nu)/(h+2)];
Fstat  = (nu-2)/nu*Fdf(2)/(Fdf(2)-2)*mF;
pFstat = 1-spm_Fcdf(Fstat,round(Fdf));

% Report on the terminal
%-----------------------------------------------------------
fprintf('F test for any effect in F image\n');
fprintf('Analysis in %s\n', dir);
fprintf('df (EoI): %.2f, df (error): %0.2f\n', h, nu);
fprintf('Mean F: %9.2f, F: %9.2f, p: %0.6f\n', mF, Fstat, pFstat);