document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1161572>Question 1161572</A>: <I><SPAN STYLE=\"word-break: break-all;\"> U.S. News & World Report carried an article concerning drug-related murders in the nation's capital. A sample of 112 days in 1987 revealed an average of three homicides per day in a increased to 4.2. If the respective standard deviations were 1.9 and 2.2 murders, does the interval suggest a difference in the incidence of homicides in 1988? Set a=0.05. Assume the population variances are equal. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #785170 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=785170\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> This is a 2 sample t-test and assumed randomness. The pop variances are equal.<BR>\n" );
document.write( "one can do t with df=222 (112-1)*2 or z because of the larger sample size.<BR>\n" );
document.write( "Both test statistics are -4.37 which is highly significant with a p-value=0.0000193.\r<BR>\n" );
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document.write( "Given that calculating pooled degrees of freedom is a lot of work by hand, it is easier to do this on a calculator for the \"correct\" t-test. In the real world, with df=217.4, z would be fine, especially when the test statistic is very large. </SPAN>\n" );
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