7.12 Exercises

Selected answers are available in Sect. D.7.

Exercise 7.1 A scientist is comparing the effects of two types of fertiliser on the yield of tomatoes (based on Klanian et al. (2018)). He plants tomato seedlings, and fertilises with Fertiliser I, and later measures the yield of tomatoes. He then immediately plants more tomato seedlings in the same field, and fertilises with Fertilizer II, and measures the yield of tomatoes.

What potential problems can you identify with the study design?

Exercise 7.2 A scientist is expecting that tap water will taste the same as bottled water in a taste test (based on Teillet et al. (2010)). The scientist provides people with a plastic cup of either bottled or tap water, and she asks them to give a rating of the taste on a scale of 1 (terrible) to 5 (fantastic).

What potential problems can you identify with the study design?

Exercise 7.3 Consider this RQ (based on Teillet et al. (2010))):

Among university students, is the taste of tap water different than the taste of bottled water?

This RQ needs some clarification, but you decide to answer this question using an experiment. How would you manage:

  1. Random allocation?
  2. Blinding?
  3. Double blinding?
  4. Finding a control?
  5. Finding a random sample?

Exercise 7.4 In a study of time spent applying sunscreen (Heerfordt et al. 2018) the Aim was to ‘determine whether time spent on sunscreen application is related to the amount of sunscreen used’ (Heerfordt et al. (2018), p. 117). The authors state this about the study design:

The volunteers were asked to apply the provided sunscreen […] the way they would normally do on a sunny day at the beach in Denmark […] The volunteers wore swimwear during the whole session. No other information was given. Participants applied sunscreen behind a curtain and were not observed during application. Measurements of time and sunscreen weight were made without the subjects’ being aware of this.

Heerfordt et al. (2018), p. 118

  1. What are the response and explanatory variables?
  2. The researchers also recorded age, height, weight and body surface area of each participant. Why would they have done this?
  3. The researchers also compared the mean values of the response variable for males and females, and the mean values of the explanatory variable for males and females. Why would they have done this?
  4. What design features are being used in the second quote?


Heerfordt IM, Torsnes LR, Philipsen PA, Wulf HC. Photoprotection by sunscreen depends on time spent on application. Photodermatology, Photoimmunology & Photomedicine. Wiley Online Library; 2018;34(2):117–21.
Klanian MG, Diaz MD, Aranda J, Juárez CR. Integrated effect of nutrients from a recirculation aquaponic system and foliar nutrition on the yield of tomatoes Solanum lycopersicum L. And Solanum pimpinellifolium. Environmental Science and Pollution Research. Springer; 2018;1–3.
Teillet E, Urbano C, Cordelle S, Schlich P. Consumer perception and preference of bottled and tap water. Journal of sensory studies. Wiley Online Library; 2010;25(3):463–80.