Demography and epidemiology: Practical use of the Lexis diagram ...
Demography and epidemiology: Practical use of the Lexis diagram ...
Demography and epidemiology: Practical use of the Lexis diagram ...
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16 8 So who needs <strong>the</strong> Cox-model?<br />
• Enables smoothing <strong>of</strong> <strong>the</strong> effects <strong>of</strong> time-scales using st<strong>and</strong>ard regression tools. In<br />
particular it allows more credible estimates <strong>of</strong> survival functions in <strong>the</strong> simple case<br />
with only time since entry as time-scale.<br />
• Enables sensible modelling <strong>of</strong> interactions between time-scales <strong>and</strong> o<strong>the</strong>r variable<br />
(<strong>and</strong> between time-scales).<br />
As <strong>the</strong> necessary computing power <strong>and</strong> s<strong>of</strong>tware is available, <strong>the</strong> computational<br />
problems encountered previously are now non-existent.<br />
However, <strong>the</strong> <strong>use</strong>r-interface to <strong>the</strong> Poisson modelling is more complex than that<br />
<strong>of</strong>fered by st<strong>and</strong>ard packages for <strong>the</strong> Cox-model. This is partly beca<strong>use</strong> <strong>the</strong> Poisson<br />
approach requires a more explicit specification <strong>of</strong> time-scales <strong>and</strong> how to model <strong>the</strong>m.<br />
The latter should however be considered an advantage from a scientific point <strong>of</strong> view,<br />
beca<strong>use</strong> it explicitly requires <strong>the</strong> researcher to make informed choices about which<br />
time-scales are relevant, how to model <strong>the</strong> effect <strong>of</strong> <strong>the</strong>m, <strong>and</strong> in particular how to<br />
report <strong>the</strong>se effects.
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