This example in Excel Help is wr
I find using the 2 Excel worksheet functions below
LOGNORMDIST(4, 3.5, 1.2) = 0.039084 NORMSDIST((LN(4 / 3.5)) / 1.2) = 0.5443013 The 2 results above do not obey the relation stated in excel Help for LOGNORMDIST: LOGNORMDIST(x, μ, σ) = NORMSDIST((ln(x) - ln(μ)) / σ) I corrected the right hand side of the above equality from the one given in Excel Help: NORMSDIST((ln(x) - μ) / σ) It seems to me that the worksheet function LOGNORMDIST is wrong. Thank you for any feedback, Eduardo ---------------- This post is a suggestion for Microsoft, and Microsoft responds to the suggestions with the most votes. To vote for this suggestion, click the "I Agree" button in the message pane. If you do not see the button, follow this link to open the suggestion in the Microsoft Web-based Newsreader and then click "I Agree" in the message pane. http://www.microsoft.com/office/comm...et.f unctions |
This example in Excel Help is wrong: LOGNORMDIST ‰ NORMSDIST
Eduardo wrote:
I find using the 2 Excel worksheet functions below LOGNORMDIST(4, 3.5, 1.2) = 0.039084 NORMSDIST((LN(4 / 3.5)) / 1.2) = 0.5443013 The 2 results above do not obey the relation stated in excel Help for LOGNORMDIST: I think it does if you correct your NORMSDIST formula accordingly. I believe the correct formula is NORMSDIST( (ln(4) - 3.5) / 1.2 ) or NORMSDIST( ln(4/exp(3.5)) / 1.2 ). This is because for LOGNORMDIST, the 2nd and 3rd parameters are the mean (m) and sd (s) of ln(x), not x. Thus, m = ln(m') and m' = exp(m), where m' is the mean of x. So ln(x)-ln(m') = ln(x/m') = ln(x/exp(m)), and ln(a)/s = ln(a^(1/s)). Help for LOGNORMDIST: LOGNORMDIST(x, μ, σ) = NORMSDIST((ln(x) - ln(μ)) / σ) I corrected the right hand side of the above equality from the one given in Excel Help: NORMSDIST((ln(x) - μ) / σ) What version of Excel are you using? Your corrected expression matches the help text that I see for Office Excel 2003. |
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