An experimental bias is a defect in the experiment which favors a particular result over the other possible results.

For example if you have a dice and you change the number three face to one. Now when you roll it (the experiment) the possible outcomes that you have will be different from the ones that you would have had if you had not changed the three.

So now you are sure never to get a the number three and the chance of getting a one is now doubled.

For example if you have a dice and you change the number three face to one. Now when you roll it (the experiment) the possible outcomes that you have will be different from the ones that you would have had if you had not changed the three.

So now you are sure never to get a the number three and the chance of getting a one is now doubled.