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Chapter 12: Problem 23

Omega-3 revisited Exercises 21 describes an experiment investigating a dietary approach to treating bipolar disorder. Researchers randomly assigned 30 subjects to two treatment groups, one group taking a high dose of omega-3 fats and the other a placebo. a) Why was it important to randomize in assigning the subjects to the two groups? b) What would be the advantages and disadvantages of using 100 subjects instead of \(30 ?\)

Short Answer

Expert verified
Randomization prevents bias; 100 subjects increase reliability but require more resources.

Step by step solution

01

Understanding Randomization Purpose

Randomization is essential in experiments to ensure each participant has an equal chance of being assigned to any group. This process helps eliminate selection bias, ensuring that the groups are comparable at the start of the experiment and any differences observed are due to the treatment and not other confounding factors.
02

Analyzing Advantages of Increasing Sample Size

Increasing the number of subjects from 30 to 100 enhances the reliability of the experiment. A larger sample size can improve the study's power, making it easier to detect a true effect of the treatment if it exists. It can also lead to more generalizable results, as the study would better represent the broader population.
03

Evaluating Disadvantages of Increasing Sample Size

While using more subjects can improve reliability and generalizability, it also increases the cost and complexity of conducting the study. More resources, including time, staff, and financial investment, are needed to manage a larger sample. This could limit the feasibility for certain researchers with restricted budgets or timelines.

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Key Concepts

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

Understanding Sample Size
Sample size plays a crucial role in the effectiveness and reliability of any experimental study. It determines how many subjects you include in your research, and this can significantly influence your results.
  • **Larger Sample Size**: Opting for a larger sample size, like 100 subjects instead of 30, generally enhances the power of a study. This can be seen as a gain in confidence when it comes to the findings. A larger group allows for more accurate estimation of the overall population effects, making the experiment's outcomes more reliable and robust.

  • **Smaller Sample Size**: On the other hand, a smaller sample demand less resources, time, and money, providing a more practical approach if you are under constraints. However, this comes with drawbacks, including less reliable results which might not adequately represent the full population's behavior.
When choosing your sample size, consider the balance between practicality and the reliability of the findings. A well-thought decision regarding sample size can lead to meaningful and actionable results.
Exploring Experimental Design
Experimental design is a blueprint for conducting a structured investigation. The design lays out the specifics of how researchers can answer the research question effectively and efficiently.
  • **Randomization**: This is a key part of experimental design. When subjects are randomly assigned to groups, like the omega-3 fats and placebo groups in the study, it helps ensure that the treatment effects are not confounded by other variables. This means that any changes in outcomes are more likely due to the treatment, rather than external biases.

  • **Control Groups**: Including a control group, like the placebo group, allows for comparison and helps in identifying the actual impact of the treatment. The difference observed between the treatment group and the control group can provide insights into the effectiveness of the treatment.
In summary, a strong experimental design includes randomization and proper control measures to minimize errors and increase the dependability of results.
Importance of Bias Reduction
Reducing bias is critical in ensuring the validity of experimental findings. Bias can skew results, leading to incorrect interpretations and conclusions.
  • **Selection Bias**: This occurs when the subjects chosen for the study are not representative of the larger population. Through random assignment, the study mentioned here aimed to mitigate selection bias, ensuring that all subjects had an equal opportunity to be included in either treatment group.

  • **Observer Bias**: An experiment can become influenced by the expectations of those conducting it. Ensuring that the researchers do not know which subjects are receiving the treatment or placebo (a double-blind design) helps reduce observer bias.
Employing strategies to minimize bias is fundamental in achieving valid and reliable experimental outcomes. It ensures that the findings are as close to reality as possible, making them more trustworthy and useful.

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Most popular questions from this chapter

Skydiving, anyone? 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,鈥� 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, double-blind, placebo-controlled study of parachute effectiveness in skydiving. (Yes, this is the sort of thing statisticians find funny.....) 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?

Read each brief report of statistical research, and identify a) whether it was an observational study or an experiment. If it was an observational study, identify (if possible) b) whether it was retrospective or prospective. c) the subjects studied and how they were selected. d) the parameter of interest. e) the nature and scope of the conclusion the study can reach. If it was an experiment, identify (if possible) b) the subjects studied. c) the factor(s) in the experiment and the number of levels for each. d) the number of treatments. e) the response variable measured. f) the design (completely randomized, blocked, or matched). g) whether it was blind (or double-blind). h) the nature and scope of the conclusion the experiment can reach. Tossing and turning Is diet or exercise effective in combating insomnia? Some believe that cutting out desserts can help alleviate the problem, while others recommend exercise. Forty volunteers suffering from insomnia agreed to participate in a month-long test. Half were randomly assigned to a special no- desserts diet; the others continued desserts as usual. Half of the people in each of these groups were randomly assigned to an exercise program, while the others did not exercise. Those who ate no desserts and engaged in exercise showed the most improvement.

Read each brief report of statistical research, and identify a) whether it was an observational study or an experiment. If it was an observational study, identify (if possible) b) whether it was retrospective or prospective. c) the subjects studied and how they were selected. d) the parameter of interest. e) the nature and scope of the conclusion the study can reach. If it was an experiment, identify (if possible) b) the subjects studied. c) the factor(s) in the experiment and the number of levels for each. d) the number of treatments. e) the response variable measured. f) the design (completely randomized, blocked, or matched). g) whether it was blind (or double-blind). h) the nature and scope of the conclusion the experiment can reach. Depression The May \(4,2000,\) issue of Science News reported that, contrary to popular belief, depressed individuals cry no more often in response to sad situations than non depressed people. Researchers studied 23 men and 48 women with major depression and 9 men and 24 women with no depression. They showed the subjects a sad film about a boy whose father has died, noting whether or not the subjects cried. Women cried more often than men, but there were no significant differences between the depressed and non depressed groups.

Shoes A running-shoe manufacturer wants to test the effect of its new sprinting shoe on 100 -meter dash times. The company sponsors 5 athletes who will try out for the 100 -meter dash in the 2016 Summer Olympic games. To test the shoe, it has all 5 runners run the 100 -meter dash with a competitor's shoe and then again with their new shoe. The company uses the difference in times as the response variable. a) Suggest some improvements to the design. b) Why might the shoe manufacturer not be able to generalize the results they find to all runners?

Diet and blood pressure An experiment that showed that subjects fed the DASH diet were able to lower their blood pressure by an average of 6.7 points compared to a group fed a "control diet." All meals were prepared by dieticians. a) Why were the subjects randomly assigned to the diets instead of letting people pick what they wanted to eat? b) Why were the meals prepared by dieticians? c) Why did the researchers need the control group? If the DASH diet group's blood pressure was lower at the end of the experiment than at the beginning, wouldn't that prove the effectiveness of that diet? d) What additional information would you want to know in order to decide whether an average reduction in blood pressure of 6.7 points was statistically significant?
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