10.19 Is the number of tornadoes increasing? The Storm Prediction Center of the National Oceanic and Atmospheric Administration maintains a database of tornadoes, floods, and other weather phenomena. Table 10.1 summarizes the annual number of tornadoes in the United States between 1953 and 2014.6

  1. (a) 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. (b) Run the simple linear regression and report the least-squares regression line.

  3. (c) A friend of yours thinks you made a mistake fitting the model because b0 is a large negative value. Explain to him why this is not a mistake.

  4. (d) Obtain the residuals and plot them versus year. Are there any unusual patterns or cases that you did not discuss in part (a)? If so, comment on them.

    TABLE 10.1: Annual Number of Tornadoes in The United States Between 1953 and 2014
    YearNumber of
    tornadoes    		YearNumber of
    tornadoes    		YearNumber of
    tornadoes    		YearNumber of
    tornadoes
    19534211969608198568420011215
    1954550197065319867642002934
    19555931971888198765620031374
    19565041972741198870220041817
    195785619731102198985620051265
    195856419749471990113320061103
    195960419759201991113220071096
    196061619768351992129820081692
    196169719778521993117620091156
    196265719787881994108220101282
    196346419798521995123520111691
    19647041980866199611732012938
    19659061981783199711482013907
    196658519821046199814492014888
    1967926198393119991340
    1968660198490720001075

  5. (e) Are the residuals approximately Normal? Justify your answer.

  6. (f) Based on the these residual checks, are you confident proceeding with inference? Explain your answer.