Error using glmfit: Second column in Y?

Hi everyone,

I'm currently trying to use glmfit like this:

B2 = glmfit(x(c,:),y,'binomial');

With y being a n x 1 matrix with 1's and 2's for group one and two. However, it keeps giving me the following error:

For the binomial distribution, Y must be a binary vector or a matrix with two columns with the number of trials in the second column.

My question is: Should I ad a second column with 1:number of observations? Example below:

y = [1,1; 1,2; 1,3; 1,4; 2,5; 2,6; 2,7; 2,8];

Best regards,

Eric

Answer 1

[Walter Roberson]

B2 = glmfit(x(c,:), y==2, 'binomial');

That is, your use of 1 and 2 is confusing it, so you need to convert those to 0 and 1.

Answer 2

[Saurabh Gupta]

As the error suggests, Y should

1) either be a binary vector i.e. a vector of 0s and 1s only (other values, like 2, are not allowed),

2) or a 2-column matrix where second column is "the number of trials" as demonstrated by the example at the following link.

https://www.mathworks.com/help/stats/glmfit.html?s_tid=answers_rc2-3_p6_MLT#btwfz5d-1

Hope this helps!

[Eric]

Dear Saurabh Gupta,

Thanks a lot for your reply. However, I've tried all the suggested ways to do it using the glmfit page.

For:

B2 = glmfit(x(c,:),y,'binomial');

The x(c,:) is a 200x12 matrix and my y is a 200x1 matrix. Is it correct to use it when you have to apply multiple features to the same model?

When I add the following to the code:

B2 = glmfit(x(c,:),[y, ntrials],'binomial');

With the ntrials being 200x1 matrix with 1's and y is either 0 or 1. However, this gives me some very weird results. Do you know what I have done wrong?

Best,

Eric