Question 317354
Without 2001,
xave={{{ 1997.8}}}
yave={{{ 7.144}}}
SSXX={{{ 14.8}}}
SSYY={{{ 13.97972}}}
SSXY={{{ 14.224}}}
b={{{ 0.961}}}
b'={{{ 1.017}}}
r^2={{{ 0.978}}}
a={{{ -1912.9}}}
{{{ highlight(y=0.961x-1912.9)}}}
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Graph that with the data points,
{{{drawing(300,300,-2,8,-2,20,
circle(1,4.7,.3),
circle(3,5.97,.3),
circle(4,7.2,.3),
circle(5,8.55,.3),
circle(6,9.3,.3),
grid(1),
graph(300,300,-2,8,-2,20,0.961x+3.334))}}}
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With 2001,
xave={{{ 1999 }}}
yave={{{9.904}}}
SSXX={{{26}}}
SSYY={{{125.9589}}}
SSXY={{{47.976}}}
b={{{1.845}}}
b'={{{0.381}}}
r^2={{{0.703}}}
a={{{-3678.71}}}
{{{highlight_green(y=1.845x-3678.71)}}}
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Graph that with the data points over the previous graph,
{{{drawing(300,300,-2,8,-2,20,
circle(1,4.7,.3),
circle(3,5.97,.3),
circle(4,7.2,.3),
circle(5,8.55,.3),
circle(6,9.3,.3),
blue(circle(7,18.5,.3)),
grid(1),
graph(300,300,-2,8,-2,20,0.961x+3.334,1.845x+0.680614))}}}
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Although the linear model captures up to 2000 well, you can't ignore 2001.
Perhaps a linear model is not the right model to use? 
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NOTE: The graph were scaled so that the years were 1,3,4,5,6,7 instead of 1995,1997,...,2001. 
The equations work with {{{x}}} being the year and {{{y}}} being the cost.