Need to fit a trendline to a Negative Exponential set of data

I have a number of data points that appear to fit a negative
exponential model. When I graph the data in Excel that is how it
looks. However, the trends that Excel allows do not appear to fit
negative functions. Can someone tell me how to modify the trend
fitting capability of Excel to handle this data.

Please post detailed steps. I am looking a cancer data that I need to
model and display.

Thanks,

oldman

Did you try to fit an exponential trendline to the data? The icon shows
exponential growth but the formula can just as well be fitted to exponential
decay.


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-------
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> wrote in message
...
>I have a number of data points that appear to fit a negative
> exponential model. When I graph the data in Excel that is how it
> looks. However, the trends that Excel allows do not appear to fit
> negative functions. Can someone tell me how to modify the trend
> fitting capability of Excel to handle this data.
>
> Please post detailed steps. I am looking a cancer data that I need to
> model and display.
>
> Thanks,
>
> oldman

Excel 2007
http://en.wikipedia.org/wiki/Biological_half-life
....isotope decays perfectly according to first order kinetics ... a
living organism follows more complex kinetics....
I suspect that you are seeing a second order rate equation curve.
Here is a comparison:
http://www.mediafire.com/file/uzuizg...06_12_09a.xlsx

Thanks for the response. It has been more than 20 years since I
worked with this stuff. What I am attempting to model the effect on
cancerous plasma cells of the drug Cytoxan. The patient has Multiple
Myeloma and has under gone two transplants and a stem cell boost. The
patient had relapsed again I is under going a new chemo regimen of
Dex, Velcade and Cytoxan. We so far have five sample points of 8.58,
5.80, 2.04, 1.42 and 1.28. The data looks like it is a decaying
exponential. The last two points have brought the patient into the
normal range but now appear to be tapering off. Each sample point is
the cancer marker for that week.

I can not seem to get the screen shot for function argument.

Though at this point there is not sufficient data to model this
situation I believe I am on the right track. I have never worked with
this capability it Excel so the reason for the post.


Hopefully, you can give me more help with how to use this capability
in Excel.

Thanks,
oldman


On Fri, 12 Jun 2009 19:34:19 -0700 (PDT), Herbert Seidenberg
> wrote:

>Excel 2007
>http://en.wikipedia.org/wiki/Biological_half-life
>...isotope decays perfectly according to first order kinetics ... a
>living organism follows more complex kinetics....
>I suspect that you are seeing a second order rate equation curve.
>Here is a comparison:
>http://www.mediafire.com/file/uzuizg...06_12_09a.xlsx

On Sat, 13 Jun 2009 13:25:56 -0700, wrote:

>
>Though at this point there is not sufficient data to model this
>situation I believe I am on the right track. I have never worked with
>this capability it Excel so the reason for the post.


List a set of numbers for an axis. List more. List them all! :-)


Let me play with the data, then you can label them however you like.

Also if you see it (one of my solutions)the way you want it, you would
see the chart characteristics as well,and be able to use it in the
future..

Hi thanks for the response. I will display what data I have which are
the first five points for the last five weeks of data since the chemo
protocol changed.

Week Kappa freelites
0 8.58
1 5.80
2 2.04
3 1.42
4 1.28
5 1.15
6 1.05
7 .99
8 .89
9 .81
10 .78


This should be enough of a start. The normal range if the disease is
under control is .33 to 1.94. These drugs are not a cure but only a
means to keep things under control. This is the sixth treatment plan
she has tried since being diagnosed almost five years ago.

Again we really appreciate the help.

oldman










On Sat, 13 Jun 2009 13:46:53 -0700, TheQuickBrownFox
> wrote:

>On Sat, 13 Jun 2009 13:25:56 -0700, wrote:
>
>>
>>Though at this point there is not sufficient data to model this
>>situation I believe I am on the right track. I have never worked with
>>this capability it Excel so the reason for the post.
>
>
> List a set of numbers for an axis. List more. List them all! :-)
>
>
> Let me play with the data, then you can label them however you like.
>
> Also if you see it (one of my solutions)the way you want it, you would
>see the chart characteristics as well,and be able to use it in the
>future..

On Sat, 13 Jun 2009 14:27:13 -0700, wrote:

>Hi thanks for the response. I will display what data I have which are
>the first five points for the last five weeks of data since the chemo
>protocol changed.
>
>Week Kappa freelites
>0 8.58
>1 5.80
>2 2.04
>3 1.42
>4 1.28
>5 1.15
>6 1.05
>7 .99
>8 .89
>9 .81
>10 .78
>
>
>This should be enough of a start. The normal range if the disease is
>under control is .33 to 1.94. These drugs are not a cure but only a
>means to keep things under control. This is the sixth treatment plan
>she has tried since being diagnosed almost five years ago.
>
>Again we really appreciate the help.
>
>oldman

Where are the negative exponents?

That exponent is one problem. I only have the time series that shows
the drug mix is working as depicted by the decline in Kappa Freelite
values. Is it possible to fit an equation to the data and thereby
determine the exponents. Its been over 20 years since I had to work
with this stuff. Until the wife got diagnosed I thought I was done
with this kind of stuff.

When she had other chemo rounds the curves looked like this data until
she would relapse. The reason why this data decays so slowly is that
the key drug is oral so the response is slower. As you can see from
the data this treatment plan is now really five weeks old and going.
When she had infusion chemo the decline in Kappa Freelite values would
occur over four or five day and she would be totally miserable for up
to three to four months.

Not sure if this helps you to help me.

thanks,
oldman


On Sat, 13 Jun 2009 16:01:33 -0700, Archimedes' Lever
> wrote:

>On Sat, 13 Jun 2009 14:27:13 -0700, wrote:
>
>>Hi thanks for the response. I will display what data I have which are
>>the first five points for the last five weeks of data since the chemo
>>protocol changed.
>>
>>Week Kappa freelites
>>0 8.58
>>1 5.80
>>2 2.04
>>3 1.42
>>4 1.28
>>5 1.15
>>6 1.05
>>7 .99
>>8 .89
>>9 .81
>>10 .78
>>
>>
>>This should be enough of a start. The normal range if the disease is
>>under control is .33 to 1.94. These drugs are not a cure but only a
>>means to keep things under control. This is the sixth treatment plan
>>she has tried since being diagnosed almost five years ago.
>>
>>Again we really appreciate the help.
>>
>>oldman
>
> Where are the negative exponents?

Excel 2007
Inserted your data into my tables.
A second order rate equation with offset
still gives the best fit.
See Sheet2/Chart2.
http://www.mediafire.com/file/kn4jey...06_12_09b.xlsx

Herbert,

First thanks for your efforts and help.

Now for a few questions if you do not mind.
1-In chart 1 was that trendline computed by Excel 2007?
2-Is it possible to have solver compute residuals? I did this
by hard for the current data and results. If we took natural logs of
the observations would we then be able to compute a linear regression
model with errors and R^2 etc?
3-Where is the offset computed?
4-Going forward the data for days 35 will become real with
this weeks blood test. Can I substitute the real Kappa value for the
guestimated value and rework the model?
5-Working in the sheet I tried to copy and paste formulas but
using RxCy format only copied constants. What needs to be done to use
normal Excel operations?

Thanks again,

Paul

On Sat, 13 Jun 2009 21:09:11 -0700 (PDT), Herbert Seidenberg
> wrote:

>Excel 2007
>Inserted your data into my tables.
>A second order rate equation with offset
>still gives the best fit.
>See Sheet2/Chart2.
>http://www.mediafire.com/file/kn4jey...06_12_09b.xlsx