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1.8: Case Study Shot Conclusion and Chapter Summary

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  • Case Study Conclusion: To Give a Shot or Not

    New mother Elena left her pediatrician’s office still unsure whether to vaccinate baby Juan. Dr. Rodriguez gave Elena a list of reputable sources where she could look up information about the safety of vaccines herself, such as the Centers for Disease Control and Prevention (CDC). Elena reads that the consensus within the scientific community is that there is no link between vaccines and autism. She finds a long list of studies published in peer-reviewed scientific journals that disprove any link. Additionally, some of the studies are “meta-analyses” that analyzed the findings from many individual studies. Elena is reassured by the fact that many different researchers, using a large number of subjects in numerous well-controlled and well-reviewed studies, all came to the same conclusion.

    Mom Child in doctor's office
    Figure \(\PageIndex{1}\): Infant on parent's lap

    Elena also went back to the author’s website that originally scared her about the safety of vaccines. She found that the author was not a medical doctor or scientific researcher, but rather was a self-proclaimed “child wellness expert.” Also, the doctor sold books and advertising on their site, some of which were related to claims of vaccine injury. Elena realized that the doctor was both an unqualified and potentially biased source of information.

    Also, Elena realized that some of the doctor's arguments were based on correlations between autism and vaccines, but, as the saying goes, “correlation does not imply causation.” For instance, the recent rise in autism rates may have occurred during the same time period as an increase in the number of vaccines given in childhood, but Elena could think of many other environmental and social factors that have also changed during this time period. There are just too many variables to come to the conclusion that vaccines, or anything else, are the cause of the rise in autism rates based on that type of argument alone. Also, Elena learned that the age of onset of autism symptoms happens to typically be around the time that the MMR vaccine is first given, so the apparent association in the timing may just be a coincidence.

    Public health, sanitation, and the use of antibiotics and vaccines have lessened the impact of infectious disease on human populations. Through vaccination programs, better nutrition, and vector control (carriers of disease), international agencies have significantly reduced the global infectious disease burden. Reported cases of measles in the United States dropped from around 700,000 a year in the 1950s to practically zero by the late 1990s and declared eradicated by the year 2000 (Figure \(\PageIndex{2}\)). Globally, measles fell 60 percent from an estimated 873,000 deaths in 1999 to 164,000 in 2008. This advance is attributed entirely to a comprehensive vaccination program.

    Measles reporting data US 1944 to 2007
    Figure \(\PageIndex{2}\): Measles cases reported in the United States, 1944-2007. From 1944 to 1963 measles cases fluctuated between 100 - 800 cases per thousand individuals. The measles vaccine was licensed in 1963 and the number of cases plummeted to less than 100 per thousand individuals. A second dose was recommended in 1988 an causes the total number of cases to fall to nearly zero.

    However, Elena came across news about a measles outbreak that originated in California in 2014, 2015, and the latest outbreak of 2019 (Figure \(\PageIndex{3}\)). Measles wasn’t just a disease of the past as she had thought! She learned that measles and whooping cough, which had previously been rare thanks to widespread vaccinations, are now on the rise, and that people choosing not to vaccinate their children seems to be one of the contributing factors. Elena realized that it is important to vaccinate their baby against these diseases, not only to protect the baby from their potentially deadly effects but to also protect others in the population.

    In her reading, Elena learns that scientists do not yet know the causes of autism, but she feels reassured by the abundance of data that disproves any link with vaccines. She thinks that the potential benefit of protecting their baby’s health against deadly diseases outweighs any unsubstantiated claims about vaccines. She will be making an appointment to get baby Juan their shots soon.

    2019 measles cases in the US
    Figure \(\PageIndex{3}\): Measles cases reported in the US as of June 2019 - 1044 cases of measles were reported in the states of Arizona, California, Colorado, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kentucky, Maine, Maryland, Massachusetts, Michigan, Missouri, New Mexico, Nevada, New Hampshire, New Jersey, New York, Oklahoma, Oregon, Pennsylvania, Texas, Tennessee, Virginia, and Washington. This is much higher than any year in the past decade where the number of cases flucuated from 55 to 667.

    Chapter Summary

    • Science is a distinctive way of gaining knowledge about the natural world that is based on the use of evidence to logically test ideas. As such, science is more of a process than a body of knowledge.
    • A scientific theory, such as the germ theory of disease, is the highest level of explanation in science. A theory is a broad explanation for many phenomena that is widely accepted because it is supported by a great deal of evidence.
    • The scientific investigation is the cornerstone of science as a process. An investigation is a procedure for gathering evidence to test a hypothesis.
    • A scientific experiment is a type of scientific investigation in which the researcher manipulates variables under controlled conditions to test expected outcomes. Experiments are the gold standard for scientific investigations and can establish causation between variables.
    • Nonexperimental scientific investigations such as observational studies and modeling may be undertaken when experiments are impractical, unethical, or impossible. Observational studies generally can establish correlation but not causation between variables.

    Chapter Summary Review

    1. Which of the following is the best example of “doing science?”
      1. memorizing the processes of the water cycle
      2. learning how to identify trees from their leaves
      3. learning the names of all the bones in the human body
      4. making observations of wildlife while hiking in the woods
    2. A scientist develops a new idea based on their observations of nature. What should they do next?
      1. think of a way to test the idea
      2. claim that they have discovered a new theory
      3. reject any evidence that conflicts with the idea
      4. look only for evidence that supports the idea
    3. Which of the following is defined as a possible answer to a scientific question?
      1. an observation
      2. data
      3. a hypothesis
      4. statistics
    4. Do scientists usually come up with a hypothesis in the absence of any observations? Explain your answer.
    5. Why does a good hypothesis have to be falsifiable?
    6. Name one scientific law.
    7. Name one scientific theory.
    8. Give an example of a scientific idea that was later discredited.
    9. Would the idea that the Earth revolves around the Sun be considered consensus science or frontier science?
    10. True or False. A scientific investigation always follows the same sequence of steps in a linear fashion.
    11. True or False. Data that does not support a hypothesis is not useful.
    12. True or False. Experimentation is the only valid type of scientific investigation.
    13. True or False. Correlation does not imply causation.
    14. Explain why science is considered an iterative process.
    15. A statistical measurement called a P-value is often used in science to determine whether or not a difference between two groups is actually significant or simply due to chance. A P-value of 0.03 means that there is a 3% chance that the difference is due to chance alone. Do you think a P-value of 0.03 would indicate that the difference is likely to be significant? Why or why not?
    16. a. Why is it important that scientists communicate their findings to others? How do they usually do this?
    17. What is a “control group” in science?
    18. In a scientific experiment, why is it important to only change one variable at a time?
    19. Which is the dependent variable – the variable that is manipulated or the variable that is being affected by the change?
    20. Which is most likely to show or disprove causation between two variables?
      1. a controlled experiment
      2. an observational study
      3. the development of a hypothesis
      4. an observation
    21. You see an ad for a “miracle supplement” called NQP3 that claims the supplement will reduce belly fat. They say it works by reducing the hormone cortisol and by providing your body with missing unspecified “nutrients”, but they do not cite any peer-reviewed clinical studies. They show photographs of three people who appear slimmer after taking the product. A board-certified plastic surgeon endorses the product on television. Answer the following questions about this product.
      1. Do you think that because a doctor endorsed the product, it really works? Explain your answer.
      2. Do you think the photographs are good evidence that the product works? Why or why not?


    1. Sad mom by dirvish, licensed CC BY 2.0 via Flickr
    2. Measles by 2over0, released into the public domain via Wikimedia Commons
    3. Measles cases by CDC, public domain
    4. Text adapted from Human Biology by CK-12 licensed CC BY-NC 3.0