91Ó°ÊÓ

The New England Journal of Medicine reported on a study of fish oil consumption in pregnant mothers and the subsequent development of asthma in their children. Read the excerpts from the abstract and answer the questions that follow: (Source: Bisgaard et al., "Fish oil-derived fatty acids in pregnancy and wheeze and asthma in offspring" New England Journal of Medicine, vol. 375 [December 2016]: \(2530-2539\), doi: \(10.1056 /\) NEJMoa1503734 Methods: We randomly assigned 736 pregnant women at 24 weeks of gestation to receive fish oil or a placebo (olive oil) daily. Neither the investigators nor the participants were aware of group assignments during follow-up for the first 3 years of the children's lives, after which there was a 2 -year follow- up period during which only the investigators were unaware of group assignments. Results: A total of 695 children were included in the trial, and \(95.5 \%\) completed the 3-year, double-blind follow-up period. The risk of persistent wheeze or asthma in the treatment group was \(16.9 \%\), versus \(23.7 \%\) in the control group, corresponding to a relative reduction of \(30.7 \%\). a. Was this a controlled experiment or an observational study? Explain how you know. b. Assuming the study was properly conducted, can we conclude that the lower rate of asthma was caused by the mother's consumption of fish oil?

Step by step solution

01

Determine the nature of the study

To determine whether the study is a controlled experiment or an observational study, you need to distinguish the two. In a controlled experiment, subjects are randomly assigned to different conditions, and in an observational study, subjects are observed without being assigned conditions. By reading the method paragraph in the abstract, it is mentioned that pregnant women are randomly assigned to receive either fish oil or a placebo. So, this is a controlled experiment.

02

Role of randomization

Randomization is an essential aspect of controlled experiments as it eliminates the chance of any potential bias from the investigator or participant that could affect the results. It helps remove the effects of any lurking variables that could skew the outcomes. In this study, 736 pregnant women are randomly assigned to receive either fish oil or a placebo, making sure that the two groups are similar except for the treatment they received, thus any difference in outcomes can be attributed to the distance in the treatment instead of any other lurking variable.

03

Investigate the cause and effect relationship

In controlled experiments where participants are randomly assigned to groups, it is possible to establish a cause and effect relationship based on the results. In this study, since the pregnancy women were randomly given either fish oil or a placebo, and it was observed that children born to mothers who consumed fish oil had lower rates of asthma, it can be concluded that the lower rate of asthma was caused by the mother's consumption of fish oil during pregnancy. But, this conclusion is dependent on the assumption that the study was properly conducted without any hidden flaws or biases.

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Key Concepts

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

Randomization

Randomization is a fundamental principle used in controlled experiments to ensure that groups being compared are similar in all respects, except for the treatment they receive. This is done by randomly assigning participants into different groups, such as treatment and control groups. The purpose of this random allocation is to eliminate any bias that might be introduced by selection, thus ensuring that the differences in outcomes are truly due to the treatment and not some other factor.

Key benefits of randomization include:

• Elimination of Bias: By assigning participants randomly, the influence of potential confounding variables is minimized. This ensures that the treatment effect is not masked or enhanced by other factors.
• Equally Distributes Random Variables: Randomization helps distribute variables equally across groups, contributing to the reliability of the results.

In the context of the study you are referring to, 736 pregnant women were randomly assigned to either receive fish oil or a placebo. This randomization ensures that each group is comparable and any observed effects, such as the reduction in asthma risk, can be more confidently attributed to the fish oil.

Cause and Effect Relationship

In scientific research, establishing a cause and effect relationship is essential to determine if one variable directly affects another. In controlled experiments, where randomization is applied, we can assess whether a treatment or intervention directly leads to an outcome. The reason cause and effect can often be asserted in such experiments is due to the controlled environment and removal of biases and external influences.

The conditions of a well-conducted controlled experiment, as outlined below, make it feasible to infer causality:

• Random Assignment: As participants are randomly assigned to groups, any pre-existing differences are fairly distributed between the treatment and control groups.
• Blinding: By keeping participants and researchers unaware of the group allocations (as seen in the double-blind method), further bias is reduced.
• Control Over Confounding Variables: Any other factors that might influence the outcome are controlled or accounted for, ensuring that changes can be linked directly to the treatment.

In the fish oil study, a cause and effect relationship was identified, assuming the study was conducted properly. The lower asthma rates observed in the children of mothers who consumed fish oil suggest a direct causal link, given the study's methodology and the use of randomization.

Asthma Study

This particular asthma study investigated the effects of fish oil consumption during pregnancy on the development of asthma in children. Conducted by Bisgaard et al., the study was published in the New England Journal of Medicine and took a unique approach by looking at prenatal influences on childhood health outcomes.

Here are some important aspects of the study:

• Study Design: The study involved 736 pregnant women who were randomly assigned to either consume fish oil or a placebo. This setup provided a clear division between treatment and control groups.
• Outcome Measured: The primary focus was on whether the children exhibited symptoms of persistent wheeze or asthma.
• Results: A significant finding was reported: children in the fish oil group had a risk reduction of about 30.7% for asthma compared to the control group.

This study's findings support the potential benefits of fish oil during pregnancy in reducing the risk of asthma in offspring. This controlled experiment allowed researchers to offer conclusions about the cause and effect of prenatal nutrition on later health issues, like asthma.