Okay, I figured it out. The mean 10-year PE is 15.93 Standard Deviation = 6.45 Mean + StDev = 22.38 Mean - StDev = 9.48 Total Data Set = 1468 Months Months Above 22.38 = 148 (10.8%) Months Below 9.48 = 185 (12.6%) Length of periods outside 1 StDev from the mean? Have a look... <A HREF="http://home.earthlink.net/~augieboo3/above1stdev.xls" target="_new">http://home.earthlink.net/~augieboo3/above1stdev.xls</A>