Question

An experiment is planned to compare three treatments applied to shirts in a test of durable press fabric treatments to produce wrinkle-free fabrics. In the past formaldehyde had been used to produce wrinkle-free fabric, but it was considered an undesirable chemical treatment. This study is to consider three alternative chemicals: (a) PCA (1-2-3 propane tricarbolic acid), (b) BTCA tetracarboxilic acid), and (c) CA (citric acid). Four shirts will be used for each of the treatments. First, the treatments are applied to the shirts, which are then subjected to simulated wear and washing in a simulation machine. The chemical treatments will not contaminate one another if they are all placed in the same washing machine during the test. The machine can hold one to four shirts in a single simulation run. At the end of the simulation run each of the shirts is measured for tear and breaking strength of the fabric and how wrinkle-free they are after being subjected to the simulated wear and washing. The comparisons among the treatments can be affected by (a) the natural variation from shirt to shirt; (b) measurement errors; (c) variation in the application of the durable press treatment; and (d) variation in the run of the simulation of wear and washing by the simulation machine. Following is a brief description of three proposed methods of conducting this simple experiment.

Method I. The shirts are divided randomly into three groups of four shirts. Each group receives a durable press treatment as one batch and then each batch is processed in one run of the simulation machine. Each run of the simulation machine has four shirts that have receive and same treatment. There are three runs of the simulation machine.

Method II. The shirts are divided randomly into three treatment groups of four shirt each, and the durable press treatments are applied independently to single shirts. The shirts are grouped into four sets of three, one shirt from each durable press treatment in each of the four sets, and each set of three so constructed is used in one run of the simulation machine. There are four runs of the simulation machine.

Method III. The shirts are divided randomly into three groups of four shirts. The durable press treatments are applied independently to single shirts. The simulation of wear and washing is done as in Method I.

a. Which method do you favor?

b. Why do you favor the method you have chosen?

c. Briefly, what are the disadvantages of the other two methods?

Answer 1

a) I will favour method II.

b) I favour method II because the shirts are grouped into four sets of three such that one shirt from each durable press treatment in each of the four sets, and each set of three so constructed is used in one run of the simulation machine. As a result this will reduce the affect of variation in the run of washing by the simulation machine .

c) The main disadvantage of method I is that each run of the simulation machine has four shirts that have receive the same treatment. As a result this will affect the comparison among the treatments because of variation in the run of washing by the simulation machine

And the main disadvantage of method III is that the durable press treatments are applied independently to single shirts which will give rise to the variation in the application of the durable press treatment . And again its each run of the simulation machine has four shirts that have receive the same treatment that will affect the comparison among the treatments because of variation in the run of washing by the simulation machine .