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Chapter 4: Problem 94

Two essential features of all statistically designed experiments are (a) compare several treatments; use the double-blind method. (b) compare several treatments; use chance to assign subjects to treatments. (c) always have a placebo group; use the double-blind method. (d) use a block design; use chance to assign subjects to treatments. (e) use enough subjects; always have a control group.

Short Answer

Expert verified
(b) Compare several treatments; use chance to assign subjects to treatments.

Step by step solution

01

Identify the Key Elements of a Statistically Designed Experiment

Statistically designed experiments are aimed at establishing cause-and-effect relationships by controlling certain variables. Two important features of such experiments are that they utilize comparisons among different treatment groups and randomness in assignment of subjects to these groups.
02

Review the Answer Choices

Examine each provided choice to see if it includes the key experimental design features: comparison of treatments and random assignment. Choices involving other concepts such as double-blind methods and block design should also be considered but are secondary.
03

Determine Which Choices Involve Comparison of Treatments

Look at each option to see if it includes the comparison of several treatments. This is a fundamental component in order to establish a control or baseline measure against which all other outcomes can be compared.
04

Determine Which Choices Use Random Assignment

Check to see if the chosen options recommend the use of chance to assign subjects to treatments. Random assignment helps in equally distributing known and unknown confounding variables across the treatment groups, lending credibility and strength to the experiment's results.
05

Select the Answer That Best Matches Both Key Experimental Features

Upon analyzing the choices, identify which one includes both "compare several treatments" and "use chance to assign subjects to treatments." These are the core elements that align with a statistically sound experimental design. In this case, the choice is (b).

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Key Concepts

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

Random Assignment
Random assignment is a crucial component in the design of statistical experiments. It involves allocating participants or subjects into different groups purely by chance. This technique seeks to eliminate bias in the distribution of both known and unknown confounding variables across the groups.
Random assignment helps ensure that each group is similar at the start of the experiment, which means any differences observed in the outcomes can be attributed to the treatments rather than external factors.
By dispersing variables randomly, it enhances the validity of the experiment.
  • Minimizes bias
  • Balances confounding variables
  • Strengthens the causal inference
Treatment Comparison
Comparing treatments is a fundamental element in any well-designed experiment. It involves testing different conditions or interventions to observe their effect.
This comparison allows researchers to gauge which treatment is most effective or if there is any significant difference among them. This approach includes establishing a baseline or control measure, which serves as a reference point.
Treatment comparison provides evidence for causality between an intervention and the outcome.
  • Facilitates understanding of treatment effectiveness
  • Establishes benchmarks for analysis
  • Essential for valid experimental results
Statistical Methods
Statistical methods are techniques used to analyze data and interpret the results of experiments. They are fundamental in validating the findings of experiments by quantifying relationships and determining the significance of observed effects.
These methods help in assessing probabilities and in making informed conclusions based on the data.
Common statistical tools include hypothesis testing, confidence intervals, and regression analysis.
  • Ensures credible and reliable conclusions
  • Helps in making predictions and generalizations
  • Validates experimental data
Control Groups
Control groups serve as the standard or baseline in experimental design, providing a point of comparison for the treatment groups. They do not receive the experimental treatment or intervention, which allows for an effective evaluation of its impact.
The use of control groups minimizes confounding factors by showing what would happen without the treatment.
A well-defined control group is pivotal in confirming the effect of the experimental condition.
  • Helps in isolating treatment effects
  • Provides a benchmark for evaluating results
  • Reduces biases and errors in experimentation

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Most popular questions from this chapter

Workers who survive a layoff of other employees at their location may suffer from "survivor guilt." A study of survivor guilt and its effects used as subjects 120 students who were offered an opportunity to earn extra course credit by doing proofreading. Each subject worked in the same cubicle as another student, who was an accomplice of the experimenters. At a break midway through the work, one of three things happened: Treatment 1 : The accomplice was told to leave; it was explained that this was because she performed poorly. Treatment 2 : It was explained that unforeseen circumstances meant there was only enough work for one person. By "chance," the accomplice was chosen to be laid off. Treatment 3: Both students continued to work after the break. The subjects' work performance after the break was compared with performance before the break. \({ }^{35}\) Describe how you would randomly assign the subjects to the treatments (a) using slips of paper. (b) using technology. (c) using Table D.

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Which of two brands (X or Y) of electric razor shaves closer? Researchers want to design and carry out an experiment to answer this question using 50 adult male volunteers. Here's one idea: Have all 50 subjects shave the left sides of their faces with the Brand X razor and shave the right sides of their faces with the Brand Y razor. Then have each man decide which razor gave the closer shave and compile the results. (a) Identify any flaws you see in the proposed design for this experiment. (b) Describe how you would design the experiment. Explain how your design addresses each of the problems you identified in part (a).
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