In a classic study examining the effect of environment on development, Kretch et al. (1962) divided a sample of infant rats into two groups. One group was housed in a stimulus-rich environment (ladders, tunnels, etc.) while the second group was housed in a stimulus-poor environment. Later, the rats' maze-learning ability was tested to see if there is an effect of environment on maze-learning ability. Below are hypothetical data from this study (dependent variable = number of errors committed in attempting to reach the end of the maze). You found an obtained statistic of 2.21.

Rich rats: 17, 10, 25, 39, 38, 41, 29, 2 9, 42 (SS = 214, M = 30)

Poor rats: 37, 27, 26, 30, 35, 43, 40, 36, 28, 38 (SS = 321, M = 34) Use the 0.01 level of significance with one tail.

A. Test and why it's used. (i.e. A z test should be used to analyze the data because there is one group of subjects, and both the population mean and the population standard deviation ( and ) are known.)

B. Concluding paragraph with APA statistical report and explanation. (i.e. It was found that the computer program significantly increases SAT scores, z = +5.76, p < 0.01, one tailed. a. This conclusion was based on the fact that z-obtained (5.76) was larger than z-critical (2.33), and a one-tailed test was performed with a 0.01 alpha level.)

C. Graph

D. Questions: 1. What is the independent variable? 2. Would the critical statistic be larger, smaller, or the same if larger samples were used? 3. What is one way you could redo the study with more Power?