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Stroke Therapy In a 2018 study reported in The New England Journal of Medicine, Johnston et al. studied the effect of a combination of the drug clopidogrel and aspirin on reducing the rate of recurrent stroke among stroke patients. Stroke patients in the study were randomly assigned to receive clopidogrel and aspirin \((n=2432)\) or a placebo and aspirin \((n=2449)\). Of those receiving clopidogrel and aspirin, 121 had another stroke. Of those receiving the placebo and aspirin, 159 had another stroke. Researchers concluded that patients with minor ischemic stroke or high-risk TIA who received a combination of clopidogrel and aspirin had a lower risk of having another stroke. a. Compare the percentage in each group who had another stroke. Based on these percentages, does it seem like clopidogrel might be effective in reducing the risk of recurrent stroke? b. Was this a controlled experiment or an observational study? c. Identify the treatment and response variables. d. State the conclusion in terms of cause and effect or explain why cause-and- effect conclusions cannot be drawn from this study.

Step by step solution

01

Calculate the Percentage

Calculate the percentage of patients who had another stroke in both the groups. The formula to use is: \((\text{Number of patients who had another stroke} / \text{Total number of patients })\times 100\% \). For the group that received clopidogrel and aspirin: \((121/2432) \times 100\% = 4.98\%\). For the group that received placebo and aspirin: \((159/2449) \times 100\% = 6.49\%\)

02

Compare the Percentages

Compare the calculated percentages. The group that received clopidogrel and aspirin had a less percentage of recurrent strokes (4.98%) compared to the group that received placebo and aspirin (6.49%). Therefore, it seems that clopidogrel might be effective in reducing the risk of recurrent stroke.

03

Determine the Type of Study

From the information given, the patients were randomly assigned to receive either clopidogrel and aspirin or a placebo and aspirin. As such, this would be classified as a controlled experiment.

04

Identify the treatment and Response Variables

In this study, the treatment variable is the drug that the patients received (either clopidogrel and aspirin or a placebo and aspirin) and the response variable is whether they had another stroke.

05

Draw a Conclusion

Since this study was an experiment with random assignment of treatments, it can be concluded that taking clopidogrel in combination with aspirin can reduce the risk of recurrent stroke. The cause-effect relationship can be established in this case.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Controlled Experiment

A controlled experiment is one where researchers introduce a treatment or condition and study its effects on a group, while keeping all other variables constant. In the context of the stroke therapy study, patients were randomly assigned to either receive a combination of clopidogrel and aspirin or a placebo with aspirin. This random assignment is vital for minimizing biases and ensuring that the two groups are comparable, which is a hallmark of a controlled experiment. By controlling these variables, the researchers aim to isolate the effect of the treatment (clopidogrel) on the risk of recurrent strokes, providing more reliable data to analyze the treatment's effectiveness.

Moreover, controlled experiments enable researchers to establish a cause-and-effect relationship. In the exercise provided, the controlled nature of the study, as evidenced by random assignment and controlled variables, supports the conclusion that the combination of clopidogrel and aspirin could be effective at reducing the rate of recurrent strokes among patients compared to just aspirin and a placebo.

Treatment and Response Variables

In any experiment, it's important to distinguish between treatment and response variables. Treatment variables are the ones that the experimenters manipulate in order to observe the effect on the outcome, which is quantified by the response variables. In the stroke study, the treatment variable is the medication provided to the patients. One group received a combination of clopidogrel and aspirin while the other was given a placebo plus aspirin.

The response variable, on the other hand, is the occurrence of recurrent strokes. By measuring this outcome across both groups, researchers can assess the impact of the treatment. Identifying these variables correctly is crucial because it ensures the experiment is designed properly and conclusions are based on the changes in the response variable that can be attributed to the treatment variable.

Percentage Calculation

The percentage calculation is fundamental for interpreting results in many studies, including medical trials. To compare the effectiveness of treatments, researchers calculate the percentage of participants experiencing an outcome, like a recurrent stroke in the stroke study. The formula mentioned in the step-by-step solution, \( (\text{Number of patients who had another stroke} / \text{Total number of patients}) \times 100\% \) is correct and crucial.

Using this formula helps in standardizing results for comparison even if there are different sample sizes. For instance, according to the exercise, approximately 4.98% of patients who took clopidogrel and aspirin had another stroke, against 6.49% of the placebo and aspirin group, clearly showing a lower occurrence in the treatment group. It demonstrates, through the calculated percentages, how effective the drug combination could be.

Cause-and-Effect Conclusions

Drawing cause-and-effect conclusions in a study is a significant step in validating a treatment's success. However, this can only be done legitimately in a well-structured controlled experiment. The stroke study provided a good basis for cause-and-effect conclusions because of its randomized design and controlled variables. Since the treatment group with clopidogrel and aspirin showed a statistically significant lower rate of recurrent strokes compared to the placebo group, we can infer a cause-and-effect relationship.

However, it's important to remember that not all studies allow for such conclusions. Only through careful design, like that of a randomized controlled trial, can scientists and doctors confidently claim that a treatment causes a specific outcome, which is the conclusion drawn in this stroke study. Understanding this concept helps in critically evaluating research and the veracity of the claims made.