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Ch. 1 - Introduction to Statistics
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470Not the one you use?Change textbook
All textbooksLarson 8th EditionCh. 1 - Introduction to StatisticsProblem 1.Q.6
Chapter 1, Problem 1.Q.6

An experiment is performed to test the effects of a new drug on attention-deficit/hyperactivity disorder (ADHD). The experimenter identifies 320 people ages 7 to 44 with ADHD to participate in the experiment. The subjects are divided into equal groups according to age. Within each group, subjects are then randomly selected to be in either the treatment group or the control group. What type of experimental design is being used for this experiment?

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1
Identify the key components of the experimental design: The experiment involves dividing subjects into groups based on age and then randomly assigning them to treatment or control groups within each age group.
Recognize that dividing subjects into groups based on a characteristic (in this case, age) is a form of blocking. Blocking is used to control for variability in the response variable that might be caused by the blocking factor (age).
Understand that within each block (age group), subjects are randomly assigned to either the treatment group (receiving the drug) or the control group (not receiving the drug). This ensures that the treatment effect can be isolated from the variability caused by age.
Conclude that this experimental design is a 'Randomized Block Design' because it combines blocking (grouping by age) with random assignment within each block.
Note that the purpose of this design is to reduce the potential confounding effect of age on the results, ensuring a more accurate assessment of the drug's effect on ADHD.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Randomized Controlled Trial (RCT)

A Randomized Controlled Trial (RCT) is a type of experimental design where participants are randomly assigned to either a treatment group or a control group. This method helps eliminate bias and ensures that the groups are comparable, allowing researchers to assess the effect of the treatment accurately. RCTs are considered the gold standard in clinical research for evaluating the efficacy of interventions.
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Stratified Sampling

Stratified sampling is a technique used to ensure that specific subgroups within a population are adequately represented in a sample. In this experiment, participants are divided into equal age groups, which allows for a more controlled comparison of the drug's effects across different age ranges. This approach enhances the validity of the findings by accounting for age-related differences in ADHD symptoms and treatment responses.
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Control Group

A control group is a baseline group in an experiment that does not receive the treatment being tested. Instead, it may receive a placebo or standard treatment, allowing researchers to compare outcomes between the treatment and control groups. This comparison is crucial for determining the effectiveness of the new drug, as it helps isolate the drug's effects from other variables that could influence the results.
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