What phenomena occurs when a researcher’s expectations or preferences about the outcome of the study influence the results obtained?

Research bias or Experimenter bias

Explanation:

Research bias or Experimenter bias is the phenomena that results when the researcher's preferences or hopes about the result influences the obtained outcomes.

This can also be explained as a result of the unconscious  and subjective effect of the researcher's hopes on the data used in an experiment or the participants of the experiment or the outcome of the related experiment.

This can be avoided by the researcher by paying attention to the records made by the participants of the experiment and not based the outcome of the experiment on the basis of the his thinking.