Four ways a scientist can reduce bias in scientific investigations?

Three ways a scientist can reduce bias include: 1) Sampling a larger pool (assuming the subjects are human) in order to broaden recorded data. 2) Making sure to sample more than one group. This means to not just sample one's friends, etc. Have a variety. 3) Scientist must also remain unbaised. This means, when performing an experiment, one cannot consider own thoughts and opinions. Make sure the designed experiment is fair!

Is this math or science am confused?