In a 2005 paper, Paul Cockshott colloquially explains the input/output 
technique for obtaining labour-values:

"If we divide the directly utilised labour by the dollar value of the 
industry's output, we get an initial figure for the amount of [direct] 
labour in each dollar of the output. For industry A we see that 0.32 units 
of labour go directly into each dollar of output. Since we already know the 
number of dollars worth of A's output used by every other industry, we can 
use this to work out the amount of indirect labour used in each industry 
when it spends a dollar on the output of industry A. This gives a second 
estimate for the labour used in each industry, which in turn gives us a 
better estimate for the number of units of labour per dollar output of all 
industries. We can repeat this process many times and as we do so, our 
estimates will converge on the true value." 
www.dcs.gla.ac.uk/~wpc/reports/rethinking.pdf

As I noted however in 2008 
http://ricardo.ecn.wfu.edu/~cottrell/ope/archive/0807/0135.html one problem 
of this iteration procedure is that it relies on the methodological 
assumption of a fixed ratio between labour time worked, paid labour time, 
and the value of gross output produced.

It is assumed, that the magnitude of the indirect labour contained in each 
part of the output sold and transferred as an input by each sector {A} to 
other sectors {B,C,D...} will be accurately determined by applying the same 
labour-output ratio established for sector A's total gross output.

Most likely this assumption is arbitrary (think of joint production, and 
qualitatively different outputs transferred by one sector to other, 
different sectors) and it introduces a margin of error, but this error is 
not corrected by additional iterations, nor can we establish what the 
magnitude of error is.

The aim of the whole exercise is to demonstrate a strong correlation between 
labour-inputs and output values, but in reality labour-inputs are derived 
from output and input magnitudes which are themselves estimated using 
numerous statistical assumptions (including the law of averages, categorical 
assumptions, valuation adjustments, and imputations for missing data).

Paul Cockshott doesn't deny the methodological problem and the problem of 
data accuracy, but he claims "what is interesting is that despite all these 
difficulties, the actual correlations between sectoral prices and values 
remains so strong." 
http://ricardo.ecn.wfu.edu/~cottrell/ope/archive/0807/0139.html  "The bottom 
line Jurrian, is that despite all of these possible sources
of error in the data we work with the results are still very good."
http://ricardo.ecn.wfu.edu/~cottrell/ope/archive/0807/0171.html

This is scientifically not really satisfactory however (some would say it's 
crap, or propaganda), because what we require specifically is a clear proof 
that the strong correlation obtained is not simply attributable to the 
chosen methodology itself (an artifact of research design and data 
constructs), and that the strong correlation obtained is superior to any 
alternative positive or negative correlations which might also be obtained.

For such a proof, it would be useful that all the data assumptions and 
methodological assumptions implied in the calculation procedure are spelled 
out, and their likely margin of error is estimated, but to my knowledge this 
has never been done, since the data sets are simply accepted as given. The 
"science" conveniently stops at the point where a result is obtained which 
appears to clinch the case being made.

Jurriaan



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