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Chapter 4: Problem 57

\(A\) study conducted by Norman Hollenberg, professor of medicine at Brigham and Women's Hospital and Harvard Medical School, involved 27 healthy people aged 18 to \(72 .\) Each subject consumed a cocoa beverage containing 900 milligrams of flavonols (a class of flavonoids) daily for 5 days. Using a finger cuff, blood flow was measured on the first and fifth days of the study. After 5 days, researchers measured what they called "significant improvement" in blood flow and the function of the cells that line the blood vessels. \({ }^{4}\) What flaw in the design of this experiment makes it impossible to say whether the cocoa really caused the improved blood flow? Explain.

Short Answer

Expert verified
Lack of a control group means improvements can't be attributed solely to cocoa.

Step by step solution

01

Identify Experiment Design

The study involves 27 healthy participants who consume a cocoa beverage containing 900 milligrams of flavonols daily for 5 days. Blood flow is measured on the first and fifth days to assess changes.
02

Recognize Lack of Control Group

The study lacks a control group for comparison. Without a control group, it's impossible to determine whether the observed improvements in blood flow were due to the cocoa consumption or other uncontrolled factors.
03

Consider Possible Confounding Variables

There could be other variables, such as diet, activity level, or existing health conditions, that might influence blood flow independently of cocoa consumption. These confounding variables can affect the results.
04

Conclude Experiment Design Flaw

The experiment's flaw is the absence of a control group, which means any observed improvements in blood flow cannot be conclusively attributed to cocoa consumption. A randomized controlled trial is needed for clearer causation conclusions.

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Key Concepts

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

Control Group
In scientific experiments, a control group is essential because it serves as a benchmark. It allows researchers to compare the treatment group (like the one consuming cocoa in the exercise) to another group that does not receive the treatment. This comparison helps establish if the effect is indeed due to the treatment, rather than other factors.
For instance, in the cocoa study, having a control group could mean one group consumes cocoa, while another consumes a placebo with no flavonols. Both groups should be similar in all major characteristics except for the treatment.
If the group consuming the cocoa shows improved blood flow compared to the control group, researchers can be more confident that cocoa is causing this change. Without a control group, any observed changes in the study could be due to a multitude of factors unrelated to the treatment.
Confounding Variables
Confounding variables are factors other than the treatment that might influence the outcome of an experiment. These variables can provide alternative explanations for the results.
In the cocoa study, confounding variables might include participants' diet, stress levels, or exercise habits, which can affect blood flow independently of cocoa consumption.
For example, if some participants were physically more active or had started a new diet during the study, these factors might improve their blood flow, clouding the true effect of cocoa.
To handle confounding variables, researchers should strive to identify and control them, possibly by ensuring the random allocation of subjects to groups, thereby evenly distributing these variables across all groups. This process helps in isolating the effect of the treatment from other influencing factors.
Randomized Controlled Trial
A randomized controlled trial (RCT) is the gold standard in experimental design. It involves randomly assigning participants to either the treatment group or the control group. This randomization helps ensure that each group is similar at the start of the experiment, thus reducing the impact of confounding variables.
The use of RCTs is especially critical when studying complex health outcomes, as it boosts the reliability of the results.
By having a control group and random assignment, researchers can observe the true effects of the treatment without interference from other factors.
In the case of the cocoa study, an RCT would mean that 27 participants are randomly split into two groups, one receiving cocoa and the other a placebo. By comparing the outcomes, the researchers could better conclude the cocoa's effects on blood flow.

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