Hi,
I sent the following answer to the SPSS list in error, so am now forwarding it on to ALLSTAT.
>Hi Dan,
>Tentatively, because playing with infinities and 0 is risky, so using a calculator:
>If first variable = 0, then exp0 = 1 and then 1/exp0 = 1.
>If first variable = 20, say, then exp20 = 485165195.4 and 1/exp20 = 0.000000009
>So, as first variable 'x' increases towards +Inf, the function 1/exp(x) tends towards 0 and does not go below 0.
>So, if x=0, 1/exp(0) =1 and if x=+Inf, 1/exp(+Inf) = 0 as required.
>This assumes that x lies between 0 and +Inf: you'd need to check with any potential -ve x's as to whether the function does what >you want it to.
>HTH
>Martin Holt
>Medical Statistician
----- Forwarded Message -----
From: Martin Holt <[log in to unmask]>
To: Dan Abner <[log in to unmask]>; "[log in to unmask]" <[log in to unmask]>
Sent: Thursday, 21 July 2011, 20:29
Subject: Re: Transformation Question XXXX
Hi Dan,
Tentatively, because playing with infinities and 0 is risky, so using a calculator:
If first variable = 0, then exp0 = 1 and then 1/exp0 = 1.
If first variable = 20, say, then exp20 = 485165195.4 and 1/exp20 = 0.000000009
So, as first variable 'x' increases towards +Inf, the function 1/exp(x) tends towards 0 and does not go below 0.
So, if x=0, 1/exp(0) =1 and if x=+Inf, 1/exp(+Inf) = 0 as required.
This assumes that x lies between 0 and +Inf: you'd need to check with any potential -ve x's as to whether the function does what you want it to.
HTH
Martin Holt
Medical Statistician
From: Dan Abner <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, 21 July 2011, 7:27
Subject: Transformation Question XXXX
Hello everyone,
I have a variable that ranges from
0 to +Inf and need to map it to a space
from 0 to 1 with an inverse relationship with the original variable (in
other words, 0 of the new variable corresponds with max(old variable) and 1
of new variable corresponds with min(old variable).
Can anyone suggest a transformation?
Thank you!
Dan
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