Question: 1. Write sentences that distinguish between a statistically significant difference and an important difference.

2. Problem revealed that there was no significant loss in the memory of rats that had 20 percent of their cortex removed. Calculate the effect size index and write an interpretation that incorporates both the effect size index and the t test

Problem: Karl Lashley (1890-1958) studied how the brain stores memories. In one experiment, rats learned a simple maze. Afterward, they were anesthetized and for half the rats, 20 percent of the cortex of the brain was removed. For the other half, no brain tissue was removed (a sham operation). The rats recovered and learned a maze. The number of errors was recorded. Name the independent variable, its levels, and the dependent variable. Analyze the data in the table and write a conclusion about the effect of a 20 percent loss of cortex on retention of memory for a simple maze.

            Percent of context removed

              0                         20

∑X         208                       252

∑X²       1706                     2212

N             40                        40