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SigmaPlot problem - (Jul/15/2007 )

Hi
I am having a terrible time with SigmaPlot.
I am trying to make a sigmoid curve for different concentrations of cAMP. I can get the curve but from the graph report I can't figure out the equation. Is there some way I can enter values and get the plot point on the graph?
Please help, I feel like an idiot but I can't seem to figure this out even using the help
Thanks

-syaniv-

QUOTE (syaniv @ Jul 16 2007, 06:52 AM)
Hi
I am having a terrible time with SigmaPlot.
I am trying to make a sigmoid curve for different concentrations of cAMP. I can get the curve but from the graph report I can't figure out the equation. Is there some way I can enter values and get the plot point on the graph?
Please help, I feel like an idiot but I can't seem to figure this out even using the help
Thanks


you can define the equation for fitting your data;

it is not simply possible to plot the data and to get a mathematics behind the graph;

so you must have an idea which equation may work; it is a question of trial and error; I have better experience with Graphpad´s Prism or Comsol´s Femlab to work out equations from data

-The Bearer-

QUOTE (syaniv @ Jul 15 2007, 10:52 PM)
Hi
I am having a terrible time with SigmaPlot.
I am trying to make a sigmoid curve for different concentrations of cAMP. I can get the curve but from the graph report I can't figure out the equation. Is there some way I can enter values and get the plot point on the graph?
Please help, I feel like an idiot but I can't seem to figure this out even using the help
Thanks


Hi,
Start by plotting your points as a scatter plot, "simple scatter" don't "connect the dots". Once you have your data points on a graph, then you need to do a regression analysis. This will draw a sigmoid curve through your points. Go to "statistics" on the tool bar and then pick regression wizard. For the equation category, you have to pick sigmoidal, then you need to pick the "equation name" . This will depend on how many parameters you have, which depends on your experiment. You can probably pick the simplest option, "sigmoidal, 3-parameters" unless you or someone else you are working with prefers differnt;y. Then you will hit next and it will ask you to select your x and y columns. Do this, hit next, and then hit finish. You will get a report now. This will be a page with a bunch of statistics and your equations.

At the top you see a column with "a, b, and Xo" . These are the values you need, with standarad error and other things listed next to them.. Scroll all the way down and find the equation under "Fit Description" and plug these values in. Also notice that sigma plot will tell you the equation as you are doing the regression analysis. You can just write it down and plug your values in.

Hope this helps. And don't feel like an idiot, I absolutely hated sigma plot until I got used to it, it just takes some getting used to. good luck!

-Vicky.ac-

QUOTE (Vicky.ac @ Jul 16 2007, 09:18 PM)
QUOTE (syaniv @ Jul 15 2007, 10:52 PM)
Hi
I am having a terrible time with SigmaPlot.
I am trying to make a sigmoid curve for different concentrations of cAMP. I can get the curve but from the graph report I can't figure out the equation. Is there some way I can enter values and get the plot point on the graph?
Please help, I feel like an idiot but I can't seem to figure this out even using the help
Thanks


Hi,
Start by plotting your points as a scatter plot, "simple scatter" don't "connect the dots". Once you have your data points on a graph, then you need to do a regression analysis. This will draw a sigmoid curve through your points. Go to "statistics" on the tool bar and then pick regression wizard. For the equation category, you have to pick sigmoidal, then you need to pick the "equation name" . This will depend on how many parameters you have, which depends on your experiment. You can probably pick the simplest option, "sigmoidal, 3-parameters" unless you or someone else you are working with prefers differnt;y. Then you will hit next and it will ask you to select your x and y columns. Do this, hit next, and then hit finish. You will get a report now. This will be a page with a bunch of statistics and your equations.

At the top you see a column with "a, b, and Xo" . These are the values you need, with standarad error and other things listed next to them.. Scroll all the way down and find the equation under "Fit Description" and plug these values in. Also notice that sigma plot will tell you the equation as you are doing the regression analysis. You can just write it down and plug your values in.

Hope this helps. And don't feel like an idiot, I absolutely hated sigma plot until I got used to it, it just takes some getting used to. good luck!


Hi Vicky.ac
Thanks for the help. When I get the graph report I do get those numbers and an equation. But I have to solve for x and I don't know how to transform the equation to find it. Isn't there an easier way to do this, like in graphpad?
Thanks

-syaniv-