6.8 Exercises

Selected answers are available in Sect. D.6.

Exercise 6.1 A study examined the relationship between diet quality and depression in Australian adolescents (Jacka et al. 2010). The researchers used a sample of 7114 adolescents aged 10–14 years old in their study, and also measured information about:

…age, gender, socioeconomic status, parental education, parental work status, family conflict, poor family management, dieting behaviours, body mass index, physical activity, and smoking…

Jacka et al. (2010), p. 435

After identifying the response and explanatory variables, which of these listed variable reasonably could be considered extraneous variables, confounding variables and lurking variables?

Exercise 6.2 A newspaper article (Anonymous 2012) reported on a study that found

Women who drank green tea at least three times a week were 14 per cent less likely to develop a cancer of the digestive system.

However, the final paragraph of the article notes that:

Nobody can say whether green tea itself is the reason, since green tea lovers are often more health-conscious in general.

Identify the explanatory and response variables, and explain that final sentence using terms introduced in this chapter.

Exercise 6.3 A study recorded the lung capacity (measured as Forced Expiratory Volume, or FEV, in litres) of children aged 3 to 19 (Tager et al. 1979; Kahn 2005), and also recorded whether not the children were smokers. One finding from the data (Dunn and Smyth 2018) is that children who smoke have a larger average FEV (i.e. larger average lung capacity) than children who do not smoke.

Name a confounding variable that may explain this surprising finding. Would it be likely that this variable is a lurking variable?


Anonymous. Green tea cuts risk of cancer. The Sunday Mail. 2012;19.
Dunn PK, Smyth GK. Generalized linear models with examples in R. Springer; 2018.
Jacka FN, Kremer PJ, Leslie ER, Berk M, Patton GC, Toumbourou JW, et al. Associations between diet quality and depressed mood in adolescents: Results from the Australian Healthy Neighbourhoods Study. Australian and New Zealand Journal of Psychiatry. 2010;44(5):435–42.
Kahn M. An exhalent problem for teaching statistics. Journal of Statistical Education. 2005;13(2).
Tager IB, Weiss ST, Rosner B, Speizer FE. Effect of parental cigarette smoking on the pulmonary function of children. American Journal of Epidemiology. 1979;110(1):15–26.