Consider the following studies: Study 1: The manager of a plastics company wante
ID: 3063331 • Letter: C
Question
Consider the following studies: Study 1: The manager of a plastics company wanted to compare the quality of plastic champagne flutes using raw materials (plastic beads) from two different suppliers (called Supplier A and Supplier B for this question). The company has four plastic moulding machines of differing ages and levels of reliability. Each of the four moulding machines is used to make 50 champagne flutes using raw materials from Supplier A and 50 using raw materials from Supplier B. The allocation of plastic beads to machines is randomised, as is the order they make the champagne flutes. A quality score is assessed for each of the champagne flutes. Study 2: Particle boards are made by mixing small particles of wood with an adhesive, forming this into sheets and baking them in an oven. A technician is interested in the effects of using different baking temperatures on the impact strength of particle board. 100 boards are randomly allocated to four different baking temperatures: 150ºC, 160ºC, 170ºC or 180ºC. After the boards are baked, they are sent to a laboratory where the impact strengths are measured. (a) Answer the following questions FOR EACH study:
(i) Identify the groups that are being compared. (I.e., what treatments or factors of interest are being compared?) DO NOT also say what is being measured to make the comparison – you do this in (ii).
(ii) What is being measured to compare these groups? ONLY describe the variable being measured. DO NOT also mention the groups being compared – you do this in (i).
(iii) Would you describe the study as an experiment or an observational study? - If it was an experiment, what part of the study design led you to this conclusion? - If it was an observational study, could an experiment have been easily carried out instead? If so, briefly explain how. If not, briefly explain why not.
(b) Could the results of a study such as Study 2 be used to argue that any overall difference in the impact strengths is due to the baking temperatures of the boards? Briefly justify your answer.
(c) Can blinding be used at all in Study 2? If so, describe how.
(d) In Study 1 blocking has been used. Briefly describe what was blocked and why it was blocked.
Explanation / Answer
i. In the first study, the first group contains champagne flutes made from the raw material of supplier A and the second group from supplier B
In the second study, groups are particle boards baked at temperatures of 150ºC, 160ºC, 170ºC and 180ºC
ii. In the first study, quality of flutes is measured and in the second study, the impact strength of boards are measured
iii. Both of them are experiments as we need to obtain the conclusion regarding the quality of raw material from both suppliers in the first study and change in impact strength with the temperature of boards
b. It can be argued that difference in impact strengths is due to the baking temperature of the boards if only the temperature is varied and all other factors such as humidity, raw material etc are the same