Final answer:
Variance in a between-subjects design can be reduced by using random assignment, incorporating a control group, and ensuring blinding. Increasing the sample size and having subjects experience all treatments with randomized order can also help control variability. Reliable differences in outcome must reflect the effect of the experimental treatment.
Step-by-step explanation:
To reduce variance in a between-subjects design, it is crucial to minimize the impact of confounding variables. One key method is the random assignment of experimental units to treatment groups, which helps to spread any potential lurking variables equally among the groups. Implementing a control group that receives a placebo treatment and ensuring researcher and subject blinding can protect against expectancy bias. To decrease the error bound while maintaining the same level of confidence in the study, it would be beneficial to increase the sample size subjects would generally produce more reliable data. Additionally, if the experiment can be structured so that all subjects experience both treatments with randomized order, it would reduce the effect of lurking variables.
In practice, maintaining the integrity of the experimental design involves ensuring that the experimental and control groups differ in only one independent variable, which is the treatment or condition being tested. As outcomes measured in the dependent variable should reflect the results of the treatments, meticulously planning the study to guard against variability not related to the treatment is crucial. Moreover, every experiment must include statistical tests to compare the collected data and ascertain if the observed differences between groups are meaningful and reliable.