Biostatistics Mini-project 1

The answers to these two problems should be written up as essays. You should write as though you were writing a methods and results section for a paper you would submit. Rephrase the question posed, write a brief summary of your results making clear what test you used (including degrees of freedom and other relevant parameters), whether the test was one or two-sided. Graphics can be very useful and make your point for you better than words. Include them when appropriate. Your write-ups should be kept short. You should NOT do every test you know and the data and discuss all possible outcomes. You SHOULD pick an appropriate test, conduct it, and report the results of it. NEVER, NEVER include raw Minitab (or other software) output. When appropriate, you can format your own table and include the relevant parts of the Minitab output. You should also comment on the experimental design and how it impacts your conclusions. If the data are observational, then there may be numerous factors impacting the significance of the test (or the lack of significance) and the results may not be due to the factor that is distinguishing between groups but by some uncontrolled factor. True experiments also differ in the quality of their design for controlling for miscellaneous factors. Mention any problems with the design you notice.

Problem 1: Did raising the speed limits in 1995 increase fatalities? The following are the data (the state name, the number of fatalities in 1995, the number in 1996, the percentage change in the number of fatalities, and whether the speed limit was increased from 55 mph or whether the 55 mph limit was retained.) 

State 1995_fatalities 1996_fatalities percent_change speed_limit
Alabama 1114 1146 2.9 increased
Alaska 87 81 -6.9 retained
Arizona 1025 994 -3 increased
Arkansas  631 615 -2.5 increased
California  4192 3989 -4.8 increased
Colorado  645 617 -4.3 increased
Connecticut  317 310 -2.2 retained
Delaware  121 116 -4.1 increased
District of Columbia  58 62 6.9 retained
Florida  2805 2753 -1.9 increased
Georgia  1488 1573 5.7 increased
Hawaii  130 148 13.8 retained
Idaho  262 258 -1.5 increased
Illinois  1586 1477 -6.9 increased
Indiana  960 984 2.5 retained
Iowa  527 465 -11.8 increased
Kansas  442 490 10.9 increased
Kentucky  849 842 -0.8 retained
Louisiana  894 902 0.9 retained
Maine  187 169 -9.6 retained
Maryland  671 608 -9.4 increased
Massachusetts  444 417 -6.1 increased
Michigan  1530 1505 -1.6 increased
Minnesota  597 576 -3.5 retained
Mississippi  868 811 -6.6 increased
Missouri  1109 1148 3.5 increased
Montana  215 200 -7 increased
Nebraska  254 293 15.4 increased
Nevada  313 348 11.2 increased
New Hampshire  118 134 13.6 retained
New Jersey  774 814 5.2 retained
New Mexico  485 485 0 increased
New York  1679 1593 -5.1 retained
North Carolina  1448 1494 3.2 retained
North Dakota  74 85 14.9 increased
Ohio  1360 1391 2.3 increased
Oklahoma  669 772 15.4 increased
Oregon  574 526 -8.4 retained
Pennsylvania  1480 1469 -0.7 increased
Rhode Island  69 69 0 increased
South Carolina  881 930 5.6 retained
South Dakota  158 175 10.8 increased
Tennessee  1259 1239 -1.6 increased
Texas  3183 3742 17.6 increased
Utah  325 321 -1.2 increased
Vermont  106 88 -17 retained
Virginia  900 877 -2.6 retained
Washington  653 712 9 increased
West Virginia  377 348 -7.7 retained
Wisconsin  745 761 2.1 retained
Wyoming  170 143 -15.9 increased

Problem 2: Do exercise 1 in Lecture 6.