Question 10.80

10.80 Yearly number of tornadoes.

The Storm Prediction Center of the National Oceanic and Atmospheric Administration maintains a database of tornadoes, floods, and other weather phenomena. Table 10.6 summarizes the annual number of tornadoes in the United States between 1953 and 2013.20

twister

  1. Make a plot of the total number of tornadoes by year. Does a linear trend over years appear reasonable? Are there any outliers or unusual patterns? Explain your answer.
  2. Run the simple linear regression and summarize the results, making sure to construct a 95% confidence interval for the average annual increase in the number of tornadoes.
  3. Obtain the residuals and plot them versus year. Is there anything unusual in the plot?
  4. Are the residuals Normal? Justify your answer.
  5. The number of tornadoes in 2004 is much larger than expected under this linear model. Also, the number of tornadoes in 2012 is much smaller than predicted. Remove these observations and rerun the simple linear regression. Compare these results with the results in part (b). Do you think these two observations should be considered outliers and removed? Explain your answer.

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Table 10.13: TABLE 10.6 Annual number of tornadoes in the United States between 1953 and 2013
Year Number of
tornadoes		 Year Number of
tornadoes		 Year Number of
tornadoes		 Year Number of
tornadoes
1953 421 1969 608 1985 684 2001 1215
1954 550 1970 653 1986 764 2002 934
1955 593 1971 888 1987 656 2003 1374
1956 504 1972 741 1988 702 2004 1817
1957 856 1973 1102 1989 856 2005 1265
1958 564 1974 947 1990 1133 2006 1103
1959 604 1975 920 1991 1132 2007 1096
1960 616 1976 835 1992 1298 2008 1692
1961 697 1977 852 1993 1176 2009 1156
1962 657 1978 788 1994 1082 2010 1282
1963 464 1979 852 1995 1235 2011 1691
1964 704 1980 866 1996 1173 2012 939
1965 906 1981 783 1997 1148 2013 908
1966 585 1982 1046 1998 1449
1967 926 1983 931 1999 1340
1968 660 1984 907 2000 1075