## 11.5 Exercises

Selected answers are available in Sect. D.11.

Exercise 11.1 A study of lime trees (Tilia cordata) recorded these variables for 385 lime trees in Russia :

• the foliage biomass, in kg;
• the tree diameter (in cm);
• the age of the tree (in years); and
• the origin of the tree (one of Coppice, Natural, or Planted).
Describe the variables in the study using the language of this chapter.

Exercise 11.2 Are these variables quantitative (discrete or continuous, and with what units of measurement?), or qualitative (nominal or ordinal, and with what levels?)?

1. Systolic blood pressure.
2. Program of enrolment.
4. Number of times a person visited the doctor last year.

Exercise 11.3 A study of body mass index and its relationship with use of social media recorded these variables (among others) from a group of 1140 participants:

1. Age (under 45; 45 to 64; 65 or over)
2. Gender (male; female)
3. Location (urban; rural)
4. Social media use (none; low; high)
5. BMI (body mass index; the body mass in kg, divided by the square of height in cm)
6. Total sitting time, in minutes per day
For each variable, determine the type of variable: quantitative (discrete or continuous, and with what units of measurement?), or qualitative (nominal or ordinal, and with what levels)?
Exercise 11.4 In a study of the influence of using ankle-foot orthoses in children with cerebral palsy , the data in Table 11.2 describe the 15 subjects. (GMFCS is used to describe the impact of cerebral palsy on their motor function, where lower levels means better functionality: the Gross Motor Function Classification System.) Describe the variables in the study.
TABLE 11.2: Describing the sample in the orthoses data set
Gender Age (years) Height (cm) Weight (kg) GMFCS
M 9 136 34.5 1
M 7 106 16.2 2
M 7 129 21.1 1
M 12 152 40.4 1
M 11 146 39.3 2
M 5 113 18.1 1
M 6 112 16.7 2
M 8 112 19.1 1
M 8 138 28.6 1
M 6 116 19.3 1
F 7 113 17.6 1
M 11 141 34.9 1
M 7 136 34.5 1
F 9 128 21.9 1
F 8 133 23.0 1

Exercise 11.5 A study of fertilizer use recorded the soil nitrogen after applying different fertilizer doses. These variables were recorded:

• the fertilizer dose, in kilograms of nitrogen per hectare;
• the soil nitrogen, in kilograms of nitrogen per hectare; and
• the fertilizer source; one of ‘inorganic’ or ‘organic.’
Describe the variables in the study.
Exercise 11.6 A study recorded the response of kangaroos to drones (one of ‘Vigilance,’ ‘No vigilance,’ ‘Flee $$<10$$m,’ or ‘Flee $$>10$$m’) and the altitude of the drone (30m, 60m, 100m or 120m). The mob size and sex of the kangaroo was also recorded. Describe the variables in the study.

Exercise 11.7 A study of people who died while taking selfies recorded the location (Table 11.3). Which of the following are the variables in the table? For each that is a variable, describe the variable.

1. The location.
2. The number of people who died at each location.
3. The percentage of people who died at each location.
TABLE 11.3: Locations of people dying while taking selfies
Number Percentage
Nature, associated environments 48 43.2
Train, railway, associated structures 22 19.9
Buildings, associated structures 17 15.3
Road, bridge, associated structures 12 10.8
Dams, associated structures 7 6.3
Fields, farms, associated structures 4 3.6
Others 1 0.9

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