Question

Researchers at the University of Pennsylvania suggest that a nasal spray derived from pheromones (chemicals emitted by animals when they are trying to attract a mate) may be beneficial in relieving symptoms of premenstrual syndrome (PMS) (Los Angeles Times, January 17 , 2003 ). a. Describe how you might design an experiment using 100 female volunteers who suffer from PMS to determine whether the nasal spray reduces PMS symptoms. b. Does your design from Part (a) include a placebo treatment? Why or why not? c. Does your design from Part (a) involve blinding? Is it single-blind or double-blind? Explain.

Short answer

The resulting experiment design can be outlined as follows: 100 female volunteers are divided into two groups by random assignment. The experiment group receives the nasal spray derived from pheromones and the control group is given a placebo saline spray. The experiment is double-blind, meaning neither the participants nor the researchers know who is given the placebo and who has the actual treatment. This design minimizes biases and allows for the differences in results to more likely be attributed to the effects of the pheromones.

Step-by-step solution

Identifying Experiment Group and Control Group

First, the 100 female volunteers who confront PMS are randomly divided into two groups evenly. One group is regarded as the experiment group, while the other group is treated as the control group. The experiment group receives the nasal spray derived from pheromones, and the control group receives a harmless saline spray which is similar in appearance and smell. Random assignment of participants into these two groups helps minimize biases and make sure that the only difference, before the trial starts, is due to chance.

Incorporating Placebo Treatment

Yes, the above design includes a placebo treatment. The control group that receives the harmless saline spray acts as the 'placebo' because the saline spray does not have any active effect on PMS symptoms. The main reason to utilize a placebo treatment is that it can help isolate the effect of the active ingredient in the nasal spray (pheromones) by accounting for psychological effects, such as the participant's expectation to feel better after receiving treatment.

Setting up Blinding

To ensure the reliability of the results, the above design would involve 'double-blinding'. This means neither the participants (single-blind) nor the researchers conducting the experiment and evaluating the results (double-blind) are aware of which group the participants are assigned. That way, the researchers' expectations or the participants' knowledge about the treatment won't influence the outcomes of the experiment.

Key concepts

Placebo Treatment

When evaluating new medical treatments, scientists must account for the psychological impact that receiving any form of treatment can have on individuals, regardless of the treatment’s active ingredients. This psychological impact is known as the placebo effect. A placebo treatment is a harmless, inactive substance or procedure that mimics the active treatment as closely as possible without having any therapeutic effect.

The control group in an experiment typically receives the placebo to act as a baseline to compare the effects of the actual treatment being tested. In our example involving the nasal spray study, the placebo is a saline spray, indistinguishable in appearance and smell from the active treatment. This is essential in avoiding biases that can occur if participants experience improvements simply because they believe they are receiving the active treatment. Presence of a placebo helps researchers determine if improvements in the experimental group are due to the treatment itself or are a result of psychological factors.

Using a placebo treatment is fundamental for establishing the efficacy of new medicinal solutions; it presents a clear-cut comparison between those who received the treatment versus the placebo, leading to more accurate conclusions about the treatment’s actual impact on health conditions, such as PMS in the study mentioned.

Blinding in Experiments

Blinding in experiments is a powerful technique used to reduce bias and increase the credibility of trial results. Bias can stem from participants’ expectations or researchers’ preconceived notions about the effectiveness of the treatment. In a blinded experiment, information about the treatments is concealed from one or more parties involved.

There are different levels of blinding: Single-blind studies hide the treatment information from participants, which means they don’t know whether they are receiving the active treatment or a placebo. Double-blind studies, which are considered more rigorous, keep both the participants and the researchers in the dark about who has received which treatment. That way, the researchers' objectivity is maintained when analyzing outcomes and interpreting data. Within our PMS study, the double-blinding method helps ensure that neither the participants' experiences nor the researchers' evaluative judgement are influenced by knowledge of the treatment allocation.

This technique is crucial for obtaining trustworthy results, as it prevents biased behavior and measurements that could skew the study’s conclusions. The integrity of blinding must be maintained throughout the study to safeguard the reliability of the results.

Randomized Control Trials

Randomized Control Trials (RCTs) are considered the gold standard in experimental design for testing the efficacy of new treatments. These trials utilize randomization to assign participants to either the treatment or the control (placebo) group. Randomization is an essential feature of RCTs and ensures that each participant has an equal chance of being placed in any group, which helps distribute confounding variables evenly among the groups.

In our exercise, the RCT would evenly divide the 100 female volunteers with PMS into two groups by chance alone. Such random assignment reduces selection bias and increases the chances that the groups are comparable at the start of the experiment. By comparing outcomes between the randomly assigned groups, researchers can make stronger inferences about the cause-and-effect relationship between the treatment and observed outcomes, such as the improvement of PMS symptoms.

RCTs not only provide more reliable evidence regarding the effectiveness of a treatment, but they also form the basis for clinical guidelines and decision-making in healthcare. Researchers, healthcare providers, and policymakers put great trust in the results of RCTs, as their randomized and controlled nature helps ensure that the findings are due to the treatment—and not other factors.