Question

A humor piece published in the British Medical Journal ("Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomized control trials," Gordon, Smith, and Pell, \(B M J, 2003: 327\) ) notes that we can't tell for sure whether parachutes are safe and effective because there has never been a properly randomized, doubleblind, placebo-controlled study of parachute effectiveness in skydiving. (Yes, this is the sort of thing statisticians find funny \(\ldots\).) Suppose you were designing such a study: a) What is the factor in this experiment? b) What experimental units would you propose? c) What would serve as a placebo for this study? d) What would the treatments be? e) What would the response variable be? f) What sources of variability would you control? g) How would you randomize this "experiment"? h) How would you make the experiment double-blind?

Short answer

The factor is parachute use; skydivers are the units; a backpack is the placebo; treatments are parachute or no parachute; the response is survival; control jump conditions; randomize assignments; keep participants and researchers blind.

Step-by-step solution

Identify the Factor

The factor in the experiment refers to the variable that is being changed or manipulated to observe its effects. In this study, the factor is whether a parachute is used or not during skydiving.

Determine Experimental Units

Experimental units are the subjects or entities on which the experiments are conducted. In this context, the experimental units would be the skydivers participating in the study.

Suggest a Placebo

A placebo is the control treatment that mimics the experimental treatment without containing the active component. In this scenario, the placebo would be a backpack that looks and feels like a parachute but does not function as one.

Define Treatments

The treatments in this study are the actual interventions that are applied for comparison. Here, the treatments are: (1) jumping with a real parachute, and (2) jumping with a placebo backpack.

Identify the Response Variable

The response variable is the outcome that is measured to determine the effect of the treatments. In this study, the response variable could be survival or the presence of trauma after the skydive.

Control Sources of Variability

To ensure accurate results, it's important to control variables that could cause differences in outcomes. Possible sources of variability to control include weather conditions, altitude of jump, and experience level of the skydivers.

Explain Randomization Process

Randomization helps eliminate bias by distributing potential differences evenly across treatment groups. Participants should be randomly assigned to either the parachute or placebo group, possibly using computer-generated random numbers.

Describe Double-Blind Process

A double-blind study ensures that neither the subjects nor the researchers know who is receiving which treatment to prevent bias. In this study, this could involve the skydivers not knowing whether their packs contain a parachute, and researchers having codes for each pack that are revealed only after the study is complete.

Key concepts

Randomized Control Trials

Randomized Control Trials (RCTs) are the gold standard in testing the efficacy of treatments in scientific studies. They involve randomly assigning participants into groups to receive different interventions, usually a treatment or a control like a placebo. This random assignment helps ensure that any differences in outcomes can be attributed specifically to the intervention, rather than pre-existing differences between groups. Randomization is key: - It reduces bias by evenly distributing unknown variables across treatment groups. This means any unforeseen factors do not skew results. - It enhances the credibility of the results, making the findings more generalizable. RCTs are crucial in fields like medicine, where understanding the true effectiveness of a drug or procedure is essential before widespread use. They provide high-quality evidence by rigorously comparing results between groups.

Placebo

A placebo is an inactive substance or treatment designed to mimic the experimental treatment in a study without having therapeutic effects. It serves as a control to help researchers observe the actual impact of the treatment being tested by providing a baseline comparison. Why use a placebo? - It isolates the effect of the treatment from psychological effects. Knowing they are receiving a treatment, participants might experience changes in conditions (like a reduction in pain) due to expectations, not because the treatment is effective. - It helps ensure that any changes in the condition of participants are due to the active drug or therapy, not influenced by factors like the natural course of the condition or participant expectations. In the context of the parachute study: using a placebo, like a backpack that looks and feels like a parachute, allows researchers to compare the true effect of the parachute itself against the strong psychological assurance it usually provides.

Double-Blind

A double-blind study design is where neither the participants nor the experimenters know who is receiving a particular treatment. This approach minimizes bias, as expectations or beliefs about the treatment cannot influence the outcome. Benefits of double-blind studies include: - Preventing researcher bias: even unconsciously, researchers might treat subjects differently depending on their knowledge of the treatment. - Limiting the placebo effect: participants do not know if they are receiving the treatment or a placebo, which helps in understanding the actual effectiveness of the treatment. To implement a double-blind design in the hypothetical parachute study, participants would be gearing up without knowing the contents of their backpack. Similarly, researchers would use coded packs, only revealed after study completion, to ensure unbiased data collection and analysis. This method is essential for maintaining objectivity and validity in experimental results.