Are serial killers more introverted than the general population? A sample of 14 serial killers serving life sentences was tested and found to have a mean introversion score of 42 with s = 6.8. If the population mean is 36, are the serial killers significantly more introverted at the .05 level? Perform the appropriate one-tailed test. t(13)=3.3, p<.05, one tailed.