Question

An article in the San Luis Obispo Tribune (September 7,1999 ) described an experiment designed to investigate the effect of creatine supplements on the development of muscle fibers. The article states that the researchers "looked at 19 men, all about 25 years of age and similar in weight, lean body mass, and capacity to lift weights. Ten were given creatine \(-25\) grams a day for the first week, followed by 5 grams a day for the rest of the study. The rest were given a fake preparation. No one was told what he was getting. All the men worked out under the guidance of the same trainer. The response variable measured was gain in fat-free mass (in percent)." a. What extraneous variables are identified in the given statement, and what strategy did the researchers use to deal with them? b. Do you think it was important that the men participating in the experiment were not told whether they were receiving creatine or the placebo? Explain. c. This experiment was not conducted in a double-blind manner. Do you think it would have been a good idea to make this a double-blind experiment? Explain.

Short answer

a. Extraneous variables could include diet, sleep patterns, and hydration. The researchers used standardized exercise regimens, using the same trainer, and controlled the amount of creatine. The control for other lifestyle factors is not described.\nb. It was crucial that the men did not know if they were getting creatine or a placebo, to prevent their knowledge from influencing the outcome.\nc. It might have been a good idea to conduct a double-blind experiment to eliminate any potential bias from the researchers, although this depends on how much scope there was for researcher-induced bias in measuring the response variable.

Step-by-step solution

Extraneous Variables and Strategies

Extraneous variables could be diet, hydration level, sleep patterns, and other lifestyle factors. These variables have the potential to affect the test outcome. The researchers used a standardized workout regimen, a consistent trainer, and controlled the serving size of creatine that each subject received, to deal with them. However, there is no mention of controlling for other extraneous variables like diet, sleep, and hydration.

Importance of Blinding in the Experiment

Yes, it was essential that the men were not aware of whether they were receiving creatine or a placebo. This is known as a single-blind experiment, which aims to prevent the subjects' knowledge of the treatment from influencing the outcome. It reduces bias, as any perceived changes could be due to psychological factors rather than the effect of the creatine.

Double-Blind Experiment Necessity

In this case, the experiment was not conducted in a double-blind manner, meaning that the researchers knew which participants were receiving creatine. It could have been helpful to conduct the experiment in a double-blind manner to eliminate any potential bias in the researchers' measurements or interactions with the subjects. However, it would depend on how the response variable was measured. If it was an objective measure that left little room for bias, then a double-blind setup might not have been necessary. However, if the measurement could be influenced by the researchers' knowledge, then a double-blind experiment would have been a good idea to maintain objective results.

Key concepts

Extraneous Variables

In statistics, extraneous variables are outside influences that might affect the outcome of an experiment. They are variables that are not intentionally studied within the experiment, but still could have an impact on the results. For example, in the creatine supplement study, factors like the subjects’ diet, hydration levels, sleep patterns, and lifestyle habits are all potential extraneous variables.

To control for these variables and ensure accurate results, researchers often take steps to minimize their influence. This is done by creating a controlled environment where these potential influences are standardized. In the creatine study, the researchers standardized the workout regimen, had a consistent trainer for all participants, and controlled the amount of creatine provided. While this approach addresses some extraneous variables, others like diet and sleep were not mentioned, suggesting that they could have affected the outcomes and possibly introduced confounding variables.

Single-Blind Experiment

A single-blind experiment is one where the participants do not know if they are receiving the treatment or a placebo. This design helps prevent participant expectations from influencing the results, known as the placebo effect. In the creatine experiment, participants received either creatine or a fake preparation (a placebo), and none were informed about which one they got.

This method is crucial to maintain psychological objectivity and to ensure that any changes observed are due to the supplement's effectiveness rather than participants' beliefs. The absence of this knowledge helps to prevent bias in the responses, providing a more accurate representation of the creatine's effect on muscle fiber development.

Double-Blind Experiment

Going beyond the single-blind approach, a double-blind experiment is a rigorous method where neither the participants nor the researchers know who is receiving the treatment or the placebo. This control is particularly useful in preventing both experimenter and participant biases.

In the case of the creatine study, having a double-blind procedure would have ensured that the researchers could not unintentionally influence the results through their interactions or expectations. This kind of bias is often subconscious and can skew the data, potentially altering the treatment's perceived effectiveness. A double-blind experiment would have added an additional layer of objectivity to the study’s findings, truly isolating the effect of the creatine from psychological variables.

Placebo Effect

The placebo effect occurs when individuals experience a perceived or real improvement in their condition despite having received a treatment that has no therapeutic value. It is a powerful psychological phenomenon that can influence experimental results and is the reason why the use of placebos is crucial in clinical trials.

In the creatine experiment, a fake preparation was used as a placebo to measure how the men’s belief in the supplement might enhance their physical performance. However, because this effect is purely psychological, the use of a placebo helps differentiate between the actual physiological impact of creatine and the psychological influence of taking a supplement. Understanding the placebo effect is key to designing experiments that accurately assess the effectiveness of a medical intervention.