Doubling Time

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PSA stands for Prostate Specific Antigen. PSA is producted by the prostate gland. PSA level often increases in case of prostate cancer, prostatitis and other prostate diseases.

PSA velocity was calculated as change from the first PSA reading, standardized
as PSA change per month.

Given:

PSA
_{1}: the first PSA reading

DT : the doubling time in month

V : the velocity

Then, V = PSA
_{1}+ 2
^{1/DT}

Number of days in a year: 365.25

Number of days in a month: 365.25/12

Curve fitting equations are used to fit your data to a theoritical curve.
Several methods exist to do this job.

One method, first transforms your data into a line, then applies to this
line the
least squares fitting method. Another method (the one used here), applies least square fitting method
directly to your data. This method was used because it weights the data
points equally. You will find some explanations with an example plot
here.

Weisstein, Eric W.
Least Squares Fitting--Exponential.From MathWorld--A Wolfram Web
Resource.

http://mathworld.wolfram.com/LeastSquaresFittingExponential.html.