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Chapter 12: Problem 17

Torn ACL Having at least one 15 -minute warm-up session per week resulted in a drastic reduction in tears in the anterior cruciate ligament (ACL). In a study involving about 4500 adolescent girls' soccer players in Sweden, one group was randomly assigned to warm up with a neuromuscular exercise session. This group had \(64 \%\) fewer ACL tears than the control group. a) Is this an experiment or an observational study? Explain why. b) Identify the treatments in this study. What is the response variable? c) Give one statistical advantage of using only Swedish girls who played soccer in this study. d) Give one statistical disadvantage of using only Swedish girls who played soccer in this study.

Short Answer

Expert verified
a) Experiment, it involves active intervention. b) Treatment: neuromuscular exercise; Response: ACL tears. c) Less variability. d) Limited generalizability.

Step by step solution

01

Determine if it is an Experiment or Observational Study

An experiment involves actively applying or withholding some condition to study its effects, while an observational study merely observes outcomes without intervention. In this case, the study randomly assigned participants to warm up with neuromuscular exercise, which indicates an active intervention. Therefore, this is an experiment.
02

Identify Treatments and the Response Variable

The treatment in this study is the neuromuscular exercise session provided to the warm-up group. The response variable is the number or rate of ACL tears experienced by the participants in both the treatment and control groups, used to measure the effect of the exercises.
03

Advantage of Using Only Swedish Girls Soccer Players

The main statistical advantage is a reduction in the variability due to biological, cultural, or sports type differences. By focusing on a homogeneous group (Swedish girls soccer players), any inherent variability that could obscure the effect of the treatment is minimized.
04

Disadvantage of Using Only Swedish Girls Soccer Players

A significant disadvantage is the lack of generalizability of the results to other populations. The findings might not be applicable to other groups such as boys, other nationalities, or players of different sports, limiting the broader application of the study results.

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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 critical component in experimental design. It refers to the process of randomly allocating study participants to either the treatment or control group. This technique ensures that each participant has an equal chance of being assigned to any group.

In the ACL study on adolescent girls' soccer players in Sweden, random assignment was used to determine who participated in the neuromuscular exercise session. This method helps eliminate bias and balances unknown confounding variables across both groups.

This approach helps ensure that any differences in ACL tear rates can be attributed to the treatment rather than other external factors. Thus, random assignment increases the validity of the experimental results.
Response Variable
In any experiment, identifying the response variable is crucial. The response variable is what researchers measure to determine the effect of the treatment.

In our experiment regarding ACL tears, the response variable is the number or rate of ACL tears among participants. This metric is crucial as it directly reflects the impact of the neuromuscular exercise intervention compared to the control group.

By focusing on the response variable, researchers can objectively assess the effectiveness of the treatment, determining whether the intervention truly reduced ACL tear occurrences.
Statistical Advantage
An advantage of focusing on a specific group in a study is a reduction in variability. This method, known as reducing between-group variability, enhances the precision of the experiment.

In the case of the ACL study, selecting only Swedish girls who play soccer minimizes biological and cultural differences that might skew results. This homogeneity means that changes in ACL tear rates are more likely due to the treatment rather than other variables.

Therefore, a homogeneous study group can provide clearer insights into the effectiveness of the treatment, offering a stronger statistical foundation for the results.
Lack of Generalizability
While focusing on a specific population can improve experimental precision, it also introduces the challenge of generalizability. Lack of generalizability refers to the difficulty in applying findings to broader or different populations.

In the ACL study, the focus on Swedish girls' soccer players limits the applicability of the results. The positive effects found in this study may not translate to boys, other nationalities, or athletes in different sports.

This limitation stresses the importance of conducting similar studies across diverse populations to ensure findings are universally applicable. Researchers must balance the need for specificity with the goal of generalizability to create widely applicable scientific knowledge.

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Most popular questions from this chapter

Low-cal dog food A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked. a) Identify the treatments, the experimental units, and the response variable. b) Describe a method of assigning treatments if this is to be a randomized block design with size of the breed as the blocking variable. c) Is blinding important in this experiment? Doubleblinding? How could blinding be conducted?

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. Dioxin Researchers have linked an increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in \(1976 .\) The study identified 981 women who lived near the site of the accident and were under age 40 at the time. Fifteen of the women had developed breast cancer at an unusually young average age of 45 Medical records showed that they had heightened concentrations of dioxin in their blood and that each tenfold increase in dioxin level was associated with a doubling of the risk of breast cancer. (Science News, Aug. 3, 2002)

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?

Tomatoes II The chapter also described a completely randomized two-factor experiment testing OptiGro fertilizer in conjunction with two different routines for watering the plants. Describe a strategy to randomly assign the 24 tomato plants to the six treatments.

Wine A 2001 Danish study published in the Archives of Internal Medicine casts significant doubt on suggestions that adults who drink wine have higher levels of "good" cholesterol and fewer heart attacks. These researchers followed a group of individuals born at a Copenhagen hospital between 1959 and 1961 for 40 years. Their study found that in this group the adults who drank wine were richer and better educated than those who did not. a) What kind of study was this? b) It is generally true that people with high levels of education and high socioeconomic status are healthier than others. How does this call into question the supposed health benefits of wine? c) Can studies such as these prove causation (that wine helps prevent heart attacks, that drinking wine makes one richer, that being rich helps prevent heart attacks, etc.)? Explain.
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