Final answer:
Counterbalancing is the technique used to reduce the impact of history on the results of a within-subjects experiment, as it systematically varies the order of treatment conditions. Random assignment ensures the equal distribution of lurking variables, and control groups along with blinding are used to prevent participant expectation from affecting the results.
Step-by-step explanation:
The manipulation of the time period between treatment conditions that reduces the chances of history influencing the results of a within-subjects experiment is counterbalancing. This methodology involves systematically varying the order in which treatment conditions are administered to control for the effects of the order itself as a confounding variable. By ensuring that each condition is presented first to some participants and second to others, counterbalancing seeks to equalize any effects that could be attributed to historical events or participants becoming more practiced or fatigued over time.
Using random assignment is a critical aspect of sound experimental design. It involves assigning subjects to different groups randomly, helping to ensure that any potential lurking variables are spread out equally among the groups. This makes it likely that the only differences between groups are those imposed by the researcher, allowing any different outcomes measured in the response variable to be attributed directly to the different treatments. Therefore, through random assignment and counterbalancing, an experiment can assert a cause-and-effect relationship between the explanatory and response variables.
When conducting a study with a placebo, a control group is typically used to balance the effects of being in an experiment with the effects of the active treatments. Blinding is also employed to reduce bias by keeping the individuals involved in the experiment uninformed about who is receiving the active treatment and who is receiving the placebo.