Learning and Memory Developmental Studies (studies of "very serious" risk of bias excluded). Note results in Wang et al., (2004) for "step-down test, number of shocks, session 2, day 30" cannot be displayed as percent change from control because the value cannot be calculated (number of shocks and standard deviation in control group is 0). However, a statistically significant increase in number of shocks was observed in the 45.3 ppm group (0 ± 0 versus 0.666 ± 21)