In January 2012, the New York Times published a story called Twin Births in the U.S., Like Never Before, in which they reported a 76 percent increase in the rate of twin births from 1980 to 2009. Here are the number of twin births each year (per 1000 live births). (www.cdc .gov/nchs/births.htm)

a) Using the data only up to 2009 (as in the NYTimes article),find the equation of the regression line for predicting the number of twin births by Years since 1980.
b) Explain in this context what the slope means.
c) Predict the number of twin births in the United States for the year 2014. Then compare your prediction to the actual value.
d) Fit a new regression model to the entire data sequence. Comment on the fit. Now plot the residuals. Are you satisfied with the model?

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Year 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Twin Birth (per 1000 live births) 18.92 19.21 19.46 19.86 19.88 20.50 21.30 21.36 21.80 22.41 22.46 23.05 23.35 23.88 24.39 24.86 25.84 26.83 Year 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Twin Birth (per 1000 live births) 28.08 28.87 29.30 30.12 31.11 31.46 32.15 32.17 32.11 32.19 32.62 33.22 33.15 33.20 33.15 33.7 33.9