Excel plots Yon x ,regression line,so in practical situation in preparation of standard curve of known concentration of proteain to OD ,
One have to plot concentration on y axis and od on x axis ,then click on to get y on x equation
but everywher in liturature this point has been ignored
when we are supose to find unknown conctration of protein from OD we are suppose to plot OD as known independent variable and concentration as dependent variable
In short , if we plot x axis OD and y axis conctration in excel and put equation and if we use this equation to calculate the unknown concentration of protein will lead to wrong answer,,
If any one has comment on same problem plz share ur ideas
Your concern is not clear at all. You are trying to find a problem in the "literature" that does not exist.
You have it backwards. Protein concentration is the independent variable (x-axis) and OD is the dependent variable (y-axis).
Oh, statistics understand numbers so when we r determing protein concentration based on od, then od become independent variable and protein concentration become dependent variable, what I mean is we have to get y on x regression line where y should be concentration and x Will be od,,, my concern @Omar is we miss this point many times, even I saw few commercial sop for std curve they were saying do it any way u like, but reality is statistics will not agree 👍
I think I understand your characterization of the dependent and independent variables in a protein concentration measurement, although I disagree with it. I have done this measurement many times, so I feel competent to comment. One prepares a standard curve consisting of several different amounts of the standard protein. One then adds the detection reagent and measures the absorbance (OD) of each sample. Generally, the OD increases with increasing amount of protein. Thus, the OD is "dependent" upon the amount of protein added. One always draws the standard curve with the amount of protein on the x-axis and the OD on the y-axis. One then uses linear or nonlinear regression, as necessary, to obtain the best-fit parameters.
The OD of the unknown sample is then used to calculate the amount of protein based on the regression equation, using OD as the y-value and calculating x. This part of the procedure may be why you think of the OD as the dependent variable.
Hi Adam,
Thanks for answer,
I totally agree last part as OD may be plotted on y axis and concentration on x axis,but one has to consider regression line x on y (what I mean is well known fact in statistics although most of time hidden in books)
My only concern was using Excel or any other competent software we use ,one has to chose regression line y on x or x on y whether u plotted ur variables in concerned axis
Plz look on images I have attached ,
reference:
Danial ,Biostatistics page 357 edition 6 ,
Rsoner,Fundamentals of biostatistics,p443,5 ed
Shah,Introduction To Biostatistics & Computer Science,page 6.2,
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