In a least-squares regression model, the residuals are assumed to be random. The following data represent the life expectancy of a male born in the given year.

The least-squares regression equation, treating year as the independent variable, is ŷ = 0.2056x - 337.1973. The residuals from left to right are

(a) Denote residuals above zero with an A and those below zero with a B to form a sequence.
(b) Test the assumption that the residuals are random at the α = 0.05 level of significance.

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Life Expectancy, y Year, x Year, x Life Expectancy, y 1999 73.9 2005 74.9 74.1 75.1 2000 2006 75.4 2001 74.2 2007 2002 74.3 2008 75.5 2003 74.5 2009 76.0 2004 74.9 2010 76.2 -0.108 0.114 0.109 0.003 -0.103 0.086 -0.119 -0.031 -0.136 0.158 -0.125 0.153