# Jackknife a statistic

### Dimitri Shvorob (view profile)

15 Apr 2007 (Updated )

(Extension of JACKKNIFE)

jstats(res,varargin)
```function[m,varargout] = jstats(res,varargin)
% JKNIFE     Jackknifed mean and variance
% INPUTS  :  res   - array or structure array output by JKNIFEP
%            field - if res is a structure array, field storing statistic x
% OUTPUTS  : m     - jackknife mean estimate
%            v     - (optional) jackknife variance estimate
% EXAMPLE  : See JKNIFEDEMO
% REF.     : Shao and Tu (1995), pp. 5-6
% AUTHOR   : Dimitri Shvorob, dimitri.shvorob@vanderbilt.edu, 4/15/07

switch nargin
case 0
error('Input argument "res" is undefined')
case 1
if isstruct(res)
error('Input argument "field" must be provided if "res" is a structure')
else
x0 = res(:,:,1);
x  = res(:,:,2:end);
end
case 2
if ~isstruct(res)
error('Input argument "field" is provided, but "res" is not a structure')
else
try
field = char(varargin);
catch
error('Input argument "field" must be a string')
end
try
x = eval(['res(1).' field]);
catch
end
n = length(res);
x  = repmat(x,[1 1 n-1]);
x0 = eval(['[res(1).' field ']']);
for m = 2:n
x(:,:,m-1) = eval(['[res(m).' field ']']);
end
end
end
n  = size(x,3);
mj = mean(x,3);
m  = n*x0 - (n-1)*mj;
if nargout > 1
s = 0;
for j = 1:n
d = x(:,:,j) - mj;
s = s + (d.^2);
end
varargout(1) = {((n-1)/n)*s};
end   ```