The myth of purchasing professionals’ expertise. More evidence on whether computers can make better procurement decisions

In a previous experiment, we have shown that risk assessments of purchasing experts are certainly not better than that of subjects untrained in purchasing, and worse than the decisions made by formal models (J. Purchas. Supply Manage. 9 (2003) 191–198). Since both these results are rather counterintuitive, we conducted a series of experiments geared at replication and extension of these findings. These new experiments show that our previous results are robust, and reveal an additional finding that is both worrying and puzzling. It actually seems to be the case that for the purchasing decision tasks in our experiments, experts perform worse with growing experience. It therefore seems that, at least for the kinds of purchasing decisions under study, it does not make much sense to use expert judgments at all. However, we show that there is a way in which expert judgments can be used in combination with formal models to improve the predictive accuracy of purchasing predictions. In our case, superior predictions are made when we combine the prediction of a formal model with the prediction of the ‘average expert’, thereby combining the robust linear trends as encapsulated in the formal model with the more intuitive configural rules used by experts. We provide several explanations for this phenomenon.     

The Multilevel Approach to Repeated Measures for Complete and Incomplete Data

Repeated measurements often are analyzed by multivariate analysis of variance (MANOVA). An alternative approach is provided by multilevel analysis, also called the hierarchical linear model (HLM), which makes use of random coefficient models. This paper is a tutorial which indicates that the HLM can be specified in many different ways, corresponding to different sets of assumptions about the covariance matrix of the repeated measurements. The possible assumptions range from the very restrictive compound symmetry model to the unrestricted multivariate model. Thus, the HLM can be used to steer a useful middle road between the two traditional methods for analyzing repeated measurements. Another important advantage of the multilevel approach to analyzing repeated measures is the fact that it can be easily used also if the data are incomplete. Thus it provides a way to achieve a fully multivariate analysis of repeated measures with incomplete data. This revised version was published online in June 2006 with corrections to the Cover Date.     

Model selection in random effects models for directed graphs using approximated Bayes factors

With the development of an MCMC algorithm, Bayesian model selection for the p ₂ model for directed graphs has become possible. This paper presents an empirical exploration in using approximate Bayes factors for model selection. For a social network of Dutch secondary school pupils from different ethnic backgrounds it is investigated whether pupils report that they receive more emotional support from within their own ethnic group. Approximated Bayes factors seem to work, but considerable margins of error have to be reckoned with.     

Comparisons of Bayesian estimation procedures for two-way contingency tables without interaction

Bayesian and empirical Bayesian estimation methods are reviewed and proposed for the row and column parameters in two-way Contingency tables without interaction. Rasch's multiplicative Poisson model for misreadings is discussed in an example. The case is treated where assumptions of exchangeability are reasonable a priori for the unknown parameters. Two different types of prior distributions are compared, It appears that gamma priors yield more tractable results than lognormal priors.     

ANTITHETIC VARIATES FOR MONTE CARLO ESTIMATION OF PROBABILITIES

This paper explores some possibilities for variance reduction by the use of antithetic variates when estimating probabilities.     

Dispute resolution and litigation in the construction industry. Evidence on conflicts and conflict resolution in The Netherlands and Germany

The construction industry is regarded to be a tough and competitive business characterized by short-term and opportunistic relations rather than being based on cooperative partnerships. In particular, conflicts and litigation have been claimed to proliferate in the construction industry. Upon closer inspection of the literature, it seems that the empirical basis of these claims is largely circumstantial. Using data on contractor–subcontractor relations in the construction industry in The Netherlands, we consider the extent to which litigation in construction is common. Then we compare the results to similar data sets on IT-purchasing both in The Netherlands and Germany, and to a data set with more general business-to-business transactions of larger Dutch and German firms. We find some evidence that the construction industry has higher percentages of transactions leading to either arbitration, suspension of the relation, or legal steps (1.6% versus 1.2, 0.4 and 0.6). The differences are however not as extreme as one might conclude based on superficial reading of the popular and scientific literature, and certainly not bigger than the differences between the other data sets.     

How is service procurement different from goods procurement? Exploring ex ante costs and ex post problems in IT procurement

Several studies suggest that, in practice, service procurement is more challenging than goods procurement. The underlying but largely implicit argument is that the procurement process for services involves higher buyer uncertainty and therefore requires extra efforts to mitigate this uncertainty. Drawing on Transaction Cost Economics, we use a database of information technology transactions to investigate the relationship between transaction characteristics and social embeddedness, and ex ante cost and ex post problems. We explore whether the same relationships hold across transactions that involve only goods versus transactions that also involve services. Our findings support conventional wisdom that managing the procurement process for transactions involving services is more challenging than for transactions involving goods. However, when controlling for typical transaction characteristics, there is no difference between transactions involving goods and transactions that also involve services.     

The ties that bind: Buyer-supplier relations in the construction industry

This study considers the consequences of Inter Organisational relations at two levels: the micro level of the individual, and the macro level of the organisation. Merging Transaction Cost Economics with theories on the Social Embeddedness of relations, the paper tackles several hypotheses about problems in buyer–supplier relations. We amend the general hypothesis, as has been put forward by other researchers, that having a common past in combination with an expected common future in business will reduce the likelihood that problems and conflicts occur. Our focus lies on whether this shared past and future can preclude problems better when the organisational relations are at the micro level. Our analyses of survey data from 448 contractor–subcontractor relations from the contractor's perspective in the construction industry reveal mixed support for effects of a shared past or future. We hardly find any of the expected positive effects of a shared past on supplier performance. However, we do find support for the hypothesis that a larger likelihood of future business with the same business partner has a stronger (negative) effect on the occurrence of problems if the expected future business is at the level of individuals (instead of at the level of organisations).