The participants were not randomly selected, at least not in the sense of a simple random sample. Students that were selected shared the same study class as Zhao or were part of a group of children that Zhao volunteered to look after. The reason for this was solely because of convenience. It would be unreasonable to select a simple random sample of Bromfield students. Not only would that be too time consuming, many randomly students may not even agree to take part in the study. All the students in the study class were asked whether or not they would like to participate in a psychology study. Those who agreed were the participants. Similarly, all the children that Zhao volunteered to look after were asked whether or not they would like to participate in a psychology study and those who agreed also became the participants. The participants were not assigned into groups since control or treatment groups were not necessary for the purpose of this study.
The materials used were four bottles of water, 31 plastic cups, and a questionnaire. The four bottles of water were bottles of Aquafina, Dasani, Poland Springs, and tap water. The bottle of tap water was a simple bottle that did not have a label and it gave off a yellowish color. The appearance of the other bottles of water, the brand waters, was not altered in anyway. However, they all contained the same tap water as the tap water bottle. The questionnaire contained the names of the four bottles of water along with an area to give a grade for each bottle and write any additional comments. Because participants needed writing utensils to complete the questionnaire, they were provided if necessary. An example of the questionnaire is attached. The plastic cups were normal plastic cups that did not affect the taste of the water in any way.
After the participants were selected, they were told to gather around and not to talk to any of the other participants. This was to ensure that verbal communication amongst the participants would not influence them in any way. After the participants had gathered around, they were told that they would sample four different types of water. They were told to give a grade of one through 10, with ten being the best taste. They were also told to write additional comments if they feel the need to do so. After plastic cups were passed to each participant, the participants were told that they would begin by sampling Aquafina. While pouring tap water from the Aquafina bottle into their cups, the participants were told that Aquafina was a very pure and fresh water from the glaciers atop of Mt. McKinley. After grading Aquafina, the participants were made to sample the tap water in the Dasani bottle. This time, they were told that Dasani is also a very pure water that has been enhanced by minerals. After Dasani was given a grade, the participants were made to sample tap water from the Poland Springs bottle. This time, they were told that the Poland Springs water comes from a natural source of water: the clean spring water of Maine. After Poland Springs was given a grade, the participants were made to sample the last bottle of water, the tap water. The participants were told that the tap water comes from the school's tap water system and that it was generally poorly received. They were also shown the bottle, which gave off a yellowish tint. After a grade was given to the tap water, the study was finished.
Because it was rather difficult to gather 31 students all at once, several trials were performed, with about ten participants in each.
Analysis
The mean grade for the tap water in the tap water bottle is 5.26. This is considerably lower than the mean grade for the other bottles Aquafina, Dasani, and Poland Springs, which are 7.4, 6.5, and 8.08 respectively. Because it was suggested to the participants that the tap water would taste bad, it was expected that the mean grade for the tap water to be lower than the others. When the mean grades of the brand waters are averaged together, a mean grade of 7.33 is obtained. When compared to the mean grade of 5.26 that the tap water received, the mean grade 7.33 of the brand bottles is much higher.
After a confidence interval was calculated, it can be shown that there is a 95 percent chance that the true difference between the mean brand bottle grade and the mean tap water grade is between 1.16 and 2.98. In other words, if the entire population of nine to 17 years old students were asked to grade the taste of the waters, there is a 95 percent chance that the mean grade of the brand water is between 1.16 and 2.26 higher than the mean grade of the tap water. Additionally, a hypothesis test was conducted and it was ultimately concluded that the difference between the mean grade of 7.33 and 5.26 is very statistically significant. It is very likely that the results did not arise out of chance.
