Final answer:
To control for confounding in study design, researchers use random assignment, control groups, blinding, and identification of lurking variables. Double-blinding is ideal to minimize bias, and in certain situations, observational studies or surveys are used.
Step-by-step explanation:
To avoid, minimize or control for confounding in the study design phase, researchers can implement several methods to ensure the validity of their experiments. One key approach is the random assignment of subjects to different treatment groups. A control group is also essential, receiving a placebo treatment that can't affect the response variable. Researchers can employ blinding, or more ideally, double-blinding, where both the subjects and the researchers do not know who receives the active treatment and who receives the placebo. Identifying and controlling for lurking variables is another critical step; this ensures that only the variable under investigation is responsible for changes in the response variable. In cases where experimentation is not possible or ethical, observational studies or surveys may be used.