# statistics

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The following data on the number of iron workers in the United States for the years 1978 through 2008 are
provided by the U.S. Bureau of Labor Statistics. Using regression techniques discussed in this section, analyze
the data for trend. Develop a scatter plot of the data and fit the trend line through the data. Discuss the strength
of the model.
Year Union members
(1000’s)
1978 17,340
1979 16,996
1980 16,975
1981 16,913
1982 17,002
1983 16,960
1984 16,740
1985 16,568
1986 16,390
1987 16,598
1988 16,748
1989 16,360
1990 16,269
1991 16,110
1992 16,211
1993 16,477
1994 16,334
1995 16,305
1996 16,145
1997 15,776
1998 15,472
1999 16,685
2000 15,359
2001 16,670
2002 16,098
2003 16,212
2004 16,316
2005 16,718
2006 16,707
2007 16,113
2008 15,128

• statistics - ,

y(predicted) = -34.92903226(X) + 86023.07742, where X = Year (1978, 1979, etc.)

The scatter plot slopes downward.

Correlation = - 0.633023997, which is consistent with a downward sloping plot. Also, the correlation is fairly strong at -0.633 suggesting the trend in iron workers have been decreasing over the last 31 years.