Answer:
a. When something other than the predictor variable influences the response variable in a quantitative study.
Step-by-step explanation:
A bias can be defined as the situation when something other than the predictor variable influences the response variable in a quantitative study. This ultimately implies that, a bias is considered to be a systematic error and as such is a deviation from the truth or fact which occurs when something other than the predictor variable is selected or influenced by the researcher.
Additionally, a predictor variable refers to an independent variable which is typically used to predict another variable and as such can be manipulated by the researcher in an experiment.