I model arterial baroreflex data that I have collected in humans using the Kent equation which is:(adsbygoogle = window.adsbygoogle || []).push({});

y=p1/(1+exp((x-p3)*p2))+p4; where Y=heart rate, X= estimated carotid sinus pressure, p1=range of Y, p2=slope coeff, p3=centerpoint on X, p4 = minimum Y.

I use Sigma Plot to do a best fit line on the points I have collected. The points are actually in six groups of 3 with one point which is the operating point. out of all of those points, the only one i know the gain at for sure is the single operating point.

What I would like to know is: Is there any way to force the best fit line through a point which I have the coordinates and a gain that the line should have while passing through that point.

Attached is a test file graph that explains my problem. the line fits the points with r^2 =0.966 but it does not go through the point (95,70) at a gain of -0.54, which is the only point and gain which is constant. Anybody know how to force fit the line to the point in Sigma Plot?

X Y

175.0000 58.0000 p1= 21.6905

179.0000 59.0000 p2= 0.1047

174.0000 62.0000 p3= 91.5081

155.0000 59.0000 p4= 59.9046

150.0000 57.0000

158.0000 62.0000

135.0000 62.0000

136.0000 63.0000

137.0000 60.0000

114.0000 63.0000

115.0000 59.0000

116.0000 60.0000

95.0000 70.0000

75.0000 78.0000

75.0000 77.0000

74.0000 79.0000

55.0000 83.0000

53.0000 80.0000

59.0000 81.0000

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# Sigma Plot, Non-linear regression, fitting a line to a set of points

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