36.4 Exercises
Selected answers are available in Sect. D.33.
Exercise 36.1 A research article (Duncan et al. 2018) examined the accuracy of step counts recorded on iPhones. The paper records this information about the selection of participants:
Participants were recruited through word of mouth and posters displayed around the [researcher’s] university. Participants were eligible if they were ambulatory, \(\ge 18\) years of age, and owned an iPhone 6 […] or newer model.
Although 33 participants were selected, the authors note some parts of the study used a smaller sample size because:
… one [subject] lost their phone during the observation period, [and] the other opted out of the […] test due to personal circumstances.
The paper notes that previous studies have been able to:
[…] demonstrate the accuracy of the iPhone pedometer function in laboratory test conditions. However, no studies have attempted to evaluate evidence […] in the field.
- What is the issue that the authors raise with previous studies?
- Why did the authors discuss the changes in sample size for some parts of the study?
- How would you describe the sampling method?
- What would you call the information about given about the subjects needing to be ambulatory and 18 years of age or over?
- Among many other things, the researchers compared the mean diference between the number of step counts recorded by manually counting steps and the iPhone-recorded number of steps. What type of test would be appropriate?
- While walking at 2.5 km/h,
the above test produced a \(P\)-value of 0.006.
What does this mean? - The sample size for the part of the study mentioned above was \(n=32\). Do you think the test will be statistically valid?
Exercise 36.2 One study of hearing loss among Iranian students (Mohammadpoorasl et al. 2018) used a cross-sectional study to explore the relationship between hearing loss and headphone use. The article states that
… 890 students were randomly selected from five schools at QUMS (Medicine, Dentistry, Nursing and Midwifery, Public Health, and Paramedical Sciences schools) using a proportional cluster sampling method…
The participants completed a hearing test and completed a Hearing Loss Questionnaire (values are between 17 and 34: higher scores indicating more severe hearing loss).
- What is the population?
- Critique the sampling method: What is the implication for interpreting the results of the study?
- Some of the results are presented in Table 36.1. What statistical test do you think was used to compare the scores for males and females?
- What are the hypotheses being tested about ‘Frequency of use?’
- Form an approximate 95% CI for the mean hearing loss score for students who use earphones.
- What information is needed to be able to form an approximate 95% CI for the difference between the hearing loss scores for females and males?
| Criterion | Levels | Sample size | Mean | Std. dev | P-value |
|---|---|---|---|---|---|
| Sex | Female | 543 | 19.37 | 2.91 | 0.009 |
| Male | 302 | 19.99 | 3.51 | ||
| Frequency of use | 0, 1 times/day | 194 | 19.2 | 2.87 | 0.001 |
| 2 to 3 times/day | 319 | 19.6 | 2.66 | ||
| More than 3 times/day | 278 | 20.2 | 3.54 | ||
| Earphone use | Yes | 745 | 19.8 | 3.08 | < 0.001 |
| No | 100 | 19 | 1.71 |
Exercise 36.3 The Abstract from a large study is given below:
OBJECTIVE: This study aims to elucidate any existing link between energy-containing liquids, as consumed in various forms within the diet, and the effect they may have on body weight or other diseases […]
METHODS: A self-administered online survey was conducted in 2496 participants from different countries, in six languages (Spanish, English, Chinese, French, German and Portuguese). Questions referred to their soft drink and water consumption habits, physical exercise performed, presence or absence of certain diseases and medication.
RESULTS: There is statistically significant difference (\(p < 0.001\)) in BMI and consumption of cola per week: those who consumed 0–3 cans a week have a lower BMI than those who consume >7 cans of cola a week […] There is greater presence of obesity (\(p < 0.001\)), gastritis (p < 0.001), constipation (\(p < 0.001\)) and mental illness (\(p = 0.003\)) among people who drink cola soft drinks.
CONCLUSION: Removal of energy-containing beverages from our diet may be an appropriate public health message to support those interested in preventing weight gain as well as other diseases.
Martín et al. (2018), p. 1
Evaluate the study using the six steps of research discussed in this book.