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Ch. 1 - Introduction to Statistics
Triola - Elementary Statistics 14th Edition
Triola14th EditionElementary StatisticsISBN: 9780137366446Not the one you use?Change textbook
Chapter 1, Problem 1.3.30

In Exercises 29–32, indicate whether the observational study used is cross-sectional, retrospective, or prospective.
Heart Health Study Samples of subjects with and without heart disease were selected, and then researchers looked back in time to determine whether they took aspirin on a regular basis.

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Identify the type of observational study by examining the timeline of data collection and analysis.
Understand that a cross-sectional study involves observing a specific point in time, without looking into the past or future.
Recognize that a retrospective study involves looking back in time, often using existing records or recollections to gather data about past events.
Note that a prospective study involves following subjects into the future to observe outcomes as they occur.
In this problem, researchers selected subjects and looked back in time to determine past behavior (aspirin use), which aligns with the characteristics of a retrospective study.

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Key Concepts

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

Observational Study

An observational study is a type of research where the investigator observes subjects and measures variables of interest without assigning treatments to the subjects. The goal is to find associations between variables, such as lifestyle factors and health outcomes, without manipulating the study environment.
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Retrospective Study

A retrospective study looks backward in time, usually using medical records and interviews with patients who already have a known outcome. Researchers identify subjects with and without a particular condition and then look back to see if there are differences in exposure to a suspected risk factor.
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Cross-sectional vs. Prospective Studies

Cross-sectional studies analyze data from a population at a specific point in time, while prospective studies follow subjects over time to observe future outcomes. Understanding these differences helps in identifying the study design, which affects the interpretation of results and potential biases.
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Related Practice
Textbook Question

In Exercises 9–20, identify which of these types of sampling is used: random, systematic, convenience, stratified, or cluster.

Highway Strength The New York State Department of Transportation evaluated the quality of the New York State Thruway by testing core samples collected at regular intervals of 1 mile.

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Textbook Question

Exercises 5–8 refer to the study of an association between which ear is used for cell phone calls and whether the subject is left-handed or right-handed. The study is reported in “Hemispheric Dominance and Cell Phone Use,” by Seidman et al., JAMA Otolaryngology—Head & Neck Surgery, Vol. 139, No. 5. The study began with a survey e-mailed to 5000 people belonging to an otology online group, and 717 surveys were returned. (Otology relates to the ear and hearing.)

Experiment or Observational Study Is the study an experiment or an observational study? Explain.

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Textbook Question

In Exercises 5–12, identify whether the given value is a statistic or a parameter.

Smart Phones In a Pew Research Center poll, a sample of adults in the United States was obtained, and it was found that 72% of them own smart phones.

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Textbook Question

In Exercises 33–36, identify which of these designs is most appropriate for the given experiment: completely randomized design, randomized block design, or matched pairs design.


West Nile Vaccine Currently, there is no approved vaccine for the prevention of infection by West Nile virus. A clinical trial of a possible vaccine is being planned to include subjects treated with the vaccine while other subjects are given a placebo.

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Textbook Question

In Exercises 5–12, identify whether the given value is a statistic or a parameter.

Drivers According to the Federal Highway Administration, there are 212 million licensed drivers in the United States.

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