Final answer:
To ensure experimental validity, it is necessary to account for lurking variables in the experimental design. These are external, uncontrolled factors that could impact the study's outcome and need to be minimized by utilizing a controlled environment, random assignment, and ideally, a random sample for participant selection.
Step-by-step explanation:
Understanding Experimental Design and Lurking Variables
When considering experimental design, it is essential to account for lurking variables. These variables are external factors not controlled in a study that could influence the outcome. To draw reliable conclusions, one would typically aim for a controlled environment where variables aside from the one being tested are kept constant. The presence of lurking variables can undermine the validity of an experiment by introducing alternative explanations for observed results, such as the case in Gary's experimental setup. In the scenarios given, factors like the amount of water, soil temperature, water loss due to evaporation, and the effect of insects are potential lurking variables that can affect the outcome and should ideally be controlled.
In studies involving humans, such as comparing test scores between genders, lurking variables may include differences in educational background, societal influences, and sample sizes. In the study of twins, differences in upbringing and whether twins are identical or fraternal are examples of lurking variables. The best practice approach is to utilize a controlled experiment with random assignment to minimize the impact of such variables. This ensures that the treatment groups only differ by the treatments applied, allowing for more scientifically sound conclusions. When assigning participants, choosing a random sample is effective because it gives everyone an equal chance of being part of the study, further isolating the explanatory variable's effect.