Add mDES for standardized mean differences

mDES.m

@@ -0,0 +1,66 @@
+function [RESULT] = mDES(GROUP1, GROUP2, TYPE)
+% Calculate the standardized mean difference effect size
+%
+%   GROUP1 and GROUP2 are numeric vectors from separate samples, groups, 
+%   time points, or contexts that you want to compare across. If TYPE is
+%   'diff' then GROUP1 and GROUP2 must have the same length.
+%
+%   TYPE is an optional parameter that specifies what standardizer should
+%   be used in the denominator of the standardized mean difference.
+%       'pool': The pooled SD using Cohen's formula (default)
+%       's1': The SD observed in GROUP1
+%       's2': The SD observed in GROUP2
+%       'diff': The SD of the observed differences between groups
+%
+%   RESULT is a scalar containing the standardized mean difference (d).
+%
+%   Example usage: mDES(females, males)
+%   Example usage: mDES(time1, time2, 'diff')
+%   Example usage: mDES(patients, controls, 's2')
+%
+%   (c) Jeffrey M. Girard, 2018
+%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+if ~isvector(GROUP1) || ~isvector(GROUP2) || ~isnumeric(GROUP1) || ~isnumeric(GROUP2)
+    disp('GROUP1 and GROUP2 must be numeric vectors.');
+    RESULT = NaN;
+    return;
+end
+
+if nargin < 3
+    TYPE = 'pool';
+end
+
+n1 = nansum(GROUP1);
+n2 = nansum(GROUP2);
+m1 = nanmean(GROUP1);
+m2 = nanmean(GROUP2);
+s1 = nanstd(GROUP1);
+s2 = nanstd(GROUP2);
+contrast = m1 - m2;
+
+if strcmpi(TYPE, 'pool')
+    v1 = nanvar(GROUP1);
+    v2 = nanvar(GROUP2);
+    vpool = (v1 * (n1 - 1) + v2 * (n2 - 1)) / (n1 + n2 - 2);
+    spool = sqrt(vpool);
+    RESULT = contrast / spool;
+elseif strcmpi(TYPE, 's1')
+    RESULT = contrast / s1;
+elseif strcmpi(TYPE, 's2')
+    RESULT = contrast / s2;
+elseif strcmpi(TYPE, 'diff')
+    if length(GROUP1) == length(GROUP2)
+        mdiff = nanmean(GROUP1 - GROUP2);
+        sdiff = nanstd(GROUP1 - GROUP2);
+        RESULT = mdiff / sdiff;
+    else
+        RESULT = NaN;
+    end
+else
+    disp('TYPE must be ''pool'', ''s1'', ''s2'', or ''diff''.');
+    RESULT = NaN;
+end
+
+end