Verification bias

Verification bias refers to a stubborn resistance to accepting the null hypothesis – the assumption that there is no inherent relationship between the variables being studied. The null hypothesis is the default position in experiments. This is what the researcher is attempting to eliminate through experimental investigation. For example, continuing to repeat an experiment until it “works” as desired, or excluding inconvenient cases or results may make the hypothesis immune to the facts. Verification bias amounts to the repression of negative results. 

Augustine Brannigan, The Use and Misuse of the Experimental Method in Social Psychology