Question 7.59
29. Two second-grade teachers, Miss Earls (who is an experienced teacher) and Mrs. Gifford (who is in her second year of teaching), were really excited about a new curriculum that utilized animations to teach science. They decided to use their classrooms for an experiment. Since Miss Earls had access to computers in her class, she used the animation lessons. Mrs. Gifford covered similar material with her students using handouts followed by discussions. After students had completed the materials, they were given a test designed by Miss Earls. There were 21 students in Miss Earls’s class and 29 students in Mrs. Gifford’s class. Miss Earls’s class scored, on average, 12 points higher on the test.
- Explain why confounding makes the results of these teachers’ study worthless. What are some of the confounding variables?
- Given that the principal would allow the 50 students in the two classes to be reassigned to these two teachers for this experiment and would allow the teachers to switch rooms, outline an experimental design to compare the two methods of science instruction. Use either Table 7.1 or technology to carry out the randomization.
29.
(a) Sample response: The type of instruction that each teacher would use was determined not by chance, but rather by the fact that only one of the teachers had computers in her classroom. Furthermore, this was the classroom of the more experienced teacher. Confounding variables are teacher experience, class size, classroom setup (computers versus no computers), and the fact that only one of the teachers drafted the test (which could be biased toward the animated science lessons).
(b) The design resembles Figure 7.3.
To choose the students, each is given a label, 1–50. Using either Excel and Rand() or the TI-84 calculator and randIntNoRep, a random sample of size 25 is chosen. Here is one possible sample with labels written in order from smallest to largest: 1, 3, 6, 9, 11, 12, 13, 14, 16, 17, 18, 19, 24, 30, 32, 33, 34, 35, 36, 38, 40, 41, 42, 43, 48.