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usually exist in practice. For example, the use of common resources in any of the activities makes direct costs associ- ated with activities interdependent.

(ii) Even in a deterministic world, if models sophisticated enough to cap- ture all these issues are used, the cost of analysis will outweigh the improve- ment in the solutions relative to the best alternatives available. In effect, appropriate pre-specification of all options is not an efficient strategy for making decisions in this context even in a deterministic world.

(iii) The world is in general highly stochas- tic, and uncertainty in this context requires fundamental changes in think- ing. Otherwise, we wind up carefully polishing a solution to a problem which has no useful relationship with reality.

In practice I believe it is important to embed what the 'theory' associated with these models tell us in the 'process' rather than in the 'models'. That is, do not attempt to model all possibilities. Model base plans and associated contingency plans as currently conceived, recog- nising uncertainty if appropriate, and use the results to diagnose

(a) planning decisions which need to be made,

(b) decision areas which require further data or analysis before planning decisions can be diagnosed or made.

In turn, use these results to iterate, gathering new data and testing alternatives.

Part of this process is asking the question "would a longer or shorter project duration be an improvement?"

R E F E R E N C E S

1. Chapman CB (1970) The optimal allocation of re- sources to a variable timescale. Opl. Res. Q. 21, 81-90.

2. Chapman CB and Del Hoyo J (1972) Progressive basic decision CPM. OpL Res. Q. 23, 345-359.

3. Kamburowski J (1995) On the minimum cost project schedule. Omega 23, 463-465.

4. Wu Y and Li C (1994) Minimal cost project networks: the cut set parallel difference method. Omega 22, 401-407.

5. Wu Y and Li C (1995) On the minimum cost project schedule---a response. Omega 23, 467.

CB Chapman (April 1995)

Department of Accounting & Management Science University of Southampton Highfield Southampton S09 5NH UK

On the Minimum Cost Project Schedule-- Note by the Editor

It is perhaps appropriate for me to offer two comments on the above material.

First, as editor, I should have noticed that the difficulty of translation, to which Professors Wu and Li implicitly refer [3], meant their note [2] included passages whose meaning in normal English usage was mistaken. I apologize to readers for not doing so.

Second, a referee strongly urged that Professor Kamburowski should name examples of textbooks which erroneously present the 'crashing algorithm'. I sympathize with the reasons, set out in a footnote in his note [1, p. 464], why Professor Kamburowski should

wish not to do so. However, he has furnished me with the names of five representative textbooks which commit the error, and I am satisfied that his point is well-made.

George Mitchell

R E F E R E N C E S

1. Kamburowski J (1995) On the minimum cost project schedule. Omega 23, 463-465.

2. Wu Y and Li C (1994) Minimal cost project networks: the cut set parallel difference method. Omega 22, 401-407.

3. Wu Y and Li C (1995) On the minimum cost project schedule---a response. Omega 23, 467.