    function ss = beetless(theta,data)
    % Beatle mortality example binomial -2*log(likelihood) function
    % -2 log(likelihood) = -2*sum( y log(p) + (n-y) log(1-p) )

    dose = data(:,1);
    n    = data(:,2);
    y    = data(:,3);

    global BEETLE_LINK

    switch BEETLE_LINK
     case 1
      % fitted probability from logistic model
      p  = 1./(1+exp(theta(1) + theta(2).*dose));
     case 2
      % loglog model
      p = 1-exp(-exp(theta(1)+theta(2).*dose));
     case 3
      % probit model
      p = nordf(theta(1) + theta(2).*dose);
    end

    ss = -2*sum(y.*log(p) + (n-y).*log(1-p));