I´m trying to run a logistic joinpoint regression utilising the ljr package.
I´ve been using the forward selection technique to get the number of knots for
the analysis, but I´m uncertain as to my results and the interpretation. The
documentation is rather brief ( in the package and the stats in medicine
article is quite technical) and without any good examples. At the moment I´m
thinking
1)find the number of knots both using forward and backward techniques and see
if they are close
2)present the annual percent change (APC) for each of the intervals, ie my
present data (1950-2010 in 5 year intervals) is giving me
Variables Coef
b0 Intercept -131.20404630
g0 t 0.06146463
g1 max(t-tau1,0) -0.51582466
g2 max(t-tau2,0) 0.43429615
Joinpoints:
1 tau1= 1990.5
2 tau2= 1995.5
APC 1950->1990=exp(0.06)=1.06-->6%
1990-1995=exp(0.06-0.51)=exp(-0.45)=0.63--> -37%
1995-2010=exp(0.06-0.51+0.43)-->-2%
3) Preferably a confidence interval for the APC should be given. However, this
I havent figured out yet.
//M
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