Croosov
☆    

Germany,
2017-01-04 21:29
(2640 d 08:25 ago)

Posting: # 16932
Views: 4,085
 

 Method comparison question [Bioanalytics]

Hello,

I have a question regarding method comparison. Passing Bablok regression is regarded as Gold-standard for method comparison. Do you know an example where it is better NOT to use Passing Bablok but another approach like Deming regression?

Thank you! :)
martin
★★  

Austria,
2017-01-09 13:09
(2635 d 16:45 ago)

@ Croosov
Posting: # 16941
Views: 3,409
 

 Method comparison question

Dear Croosov,

Both Deming and Bablok approaches assume a linear relation where Deming has another assumption on the ratio of errors.

However, I can highly recommend the following book which shows also approaches how to deal with replicates typically available in bio analytical studies.

Title: Comparing Clinical Measurement Methods: A Practical Guide
Author: Bendix Carstensen
Publisher: Wiley, 2010
ISBN: 0470683007, 9780470683002
Length: 176 pages

hope this helps

Martin


Edit: 204 €‽ Must be full of wisdom! SCNR [Helmut]
mittyri
★★  

Russia,
2017-01-11 12:54
(2633 d 17:00 ago)

@ martin
Posting: # 16943
Views: 3,328
 

 Method comparison question

Dear Croosov and Martin,

Full ACK with Martin.
I would add that the authors of this book surprisingly did not mention Bablok approach at all (or I didn't find it).
Regarding Deming they are also not optimistic:
Deming regression is of limited practical use because it requires a priori knowledge of the ratio of the variances, which is rarely available without replicate measurements by each method. And in that case the model is actually identifiable (see Section 7) and hence Deming regression is superfluous.
Deming regression can be used as a second step in the case where replicate measurements are made. The first step is to use the replicates to estimate the method-specific residual variances, and the second is Deming regression using the mean of replicates to estimate the relationship between methods


I think you also had a look at this article:
Validity of linear regression in method comparison studies: is it limited by the statistical model or the quality of the analytical input data?

As far as I understand Bablok approach is robust (as non-parametric) but sensitive to the non-linearity.

Sorry if I'm writing about some simple things

Kind regards,
Mittyri
Helmut
★★★
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Homepage
Vienna, Austria,
2017-01-11 14:03
(2633 d 15:52 ago)

@ mittyri
Posting: # 16944
Views: 3,351
 

 Method comparison opinion

Dear all,

just put in my two cents.

Deming regression is of limited practical use because it requires a priori knowledge of the ratio of the variances, which is rarely available without replicate measurements by each method.


If one is seriously interested in comparing methods I don’t see why replicates should not be measured. Theoretically the ideal weighting in regression is 1/σ2. The commonly applied 1/x, 1/y, :blahblah: are only lousy compromises if replicates are not available.

Panos Macheras told me that he once published a paper about Deming’s regression where the variance-ratio is estimated by the following approach:
  • Run Deming’s regressions for an arbitrary – but wide – range of variance-ratios (from very low to very high). The theoretical limits would be OLS y|x and x|y – where the entire error lies either in y or x, respectively.
  • Calculate the area between the confidence bands around the regressions.
  • The model with the minimum area gives the ‘best’ estimate of the variance-ratio.
This approach does not require replicates.

Deming regression can be used as a second step in the case where replicate measurements are made. The first step is to use the replicates to estimate the method-specific residual variances, and the second is Deming regression using the mean of replicates to estimate the relationship between methods


I don’t like this idea. Working with means would decrease the degrees of freedom of the model. If one has a priori specifications (e.g., intercept n.s. ≠ 0 and/or slope n.s. ≠ 1) with this approach the chance to pass the method comparison would increase.

❝ As far as I understand Bablok approach is robust (as non-parametric) but sensitive to the non-linearity.


Yes. Although I’m a fan-boy of non-parametrics here I would be conservative. If there are outliers (i.e., methods do not agree at certain values) IMHO, this fact needs to be explored rather than ignored.

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