BOX 7.4
Which Water Tastes Better?
The seventh- and eighth-grade students in a Haitian Creole bilingual
program wanted to find the "truth" of a belief held by most of their
classmates: that drinking water from the fountain on the third floor,
where the junior high was located, was superior to the water from the
other fountains in their school. Challenged by their teacher, the
students set out to determine whether they actually preferred the water
from the third floor or only thought they did.
As a first step, the
students designed and took a blind taste test of the water from
fountains on all three floors of the building. They found, to their
surprise, that two-thirds of them chose the water from the first-floor
fountain, even though they all said that they preferred drinking from
the third-floor fountain. The students did not believe the data. They
held firmly to their beliefs that the first-floor fountain was the worst
because "all the little kids slobber in it." (The first-floor fountain
is located near the kindergarten and first-grade classrooms.) Their
teacher was also suspicious of the results because she had expected no
differences among the three water fountains. These beliefs and
suspicions motivated the students to conduct a second taste test with a
larger sample drawn from the rest of the junior high.
The students decided
where, when, and how to run their experiment. They discussed
methodological issues: How to collect the water, how to hide the
identity of the sources, and, crucially, how many fountains to include.
They decided to include the same three fountains as before so that they
could compare results.
They worried about bias in the voting process: What if some students
voted more than once? Each student in the class volunteered to organize
a piece of the experiment. About 40 students participated in the blind
taste test. When they analyzed their data, they found support for their
earlier results: 88 percent of the junior high students thought
they preferred water from the third-floor fountain, but 55 percent
actually chose the water from the first floor (a result of 33 percent
would be chance).
Faced with this
evidence, the students' suspicions turned to curiosity. Why was the
water from the first-floor fountain preferred? How can they determine
the source of the preference? They decided to analyze the school's
water along several dimensions, among them acidity, salinity,
temperature, and bacteria. They found that all the fountains had
unacceptably high levels of bacteria. In fact, the first-floor fountain
(the one most preferred) had the highest bacterial count. They also
found that the water from the first-floor fountain was 20 degrees
(Fahrenheit) colder than the water from fountains on the other floors.
Based on their findings, they concluded that temperature was probably a
deciding factor in taste preference. They hypothesized that the water
was naturally cooled as it sat in the city's underground pipes during
the winter months (the study was conducted in February) and warmed as it
flowed from the basement to the third floor.
SOURCE: Rosebery et al. (1992).