Introduction Case Study 4: Theory-testing research: testing a probabilistic relation

deliver their goods have higher distribution costs. For some retailers this increase in costs might be relatively much more than for other retailers, depending on their distribution strategy, such as the number of stops per roundtrip.

7.2.2 Theory

7.2.2.1 Object of study

The object of study is distribution activities by retailers. This is the same object of study as in Case Study 3.

7.2.2.2 Concepts

The concepts of interest are: ■ Distribution strategy. This includes the following five dimen- sions: a the number of stops per roundtrip which number will correlate with the number of occasions that a time access win- dow could be encountered during one roundtrip, b vehicle capacity which influences the possible amount of goods car- ried in one vehicle roundtrip and with that the drop-size and the number of drops, c stopping time which is an indicator for the time that will be used within time window areas, d the distance of the retailer’s shops from the distribution centre, and e self-imposed time windows such as a policy to deliver only after or before shopping hours, or a policy to deliver only when staff is available to receive the goods. ■ Time access window pressure. This pressure consists of a the num- ber of windows number of areas in which time access windows are present, and b the lengths of these time windows. ■ Total distribution costs. In the present chapter we use only one indicator for distribution costs, which is the total costs in terms of money which results from the four dimensions that were used as indicators of distribution costs in the previous chapter.

7.2.2.3 Propositions

Our theory states that the higher the value of a retailer on a dimension of distribution strategy the more likely it is that the retailer is more “sensitive to time window pressure”. In other words, retailers with a higher value on a dimension of strategy such as a higher number of stops per roundtrip will often have a relatively higher increase in dis- tribution costs that occur with a given change in time access window pressure than retailers with a lower value on that dimension of distri- bution strategy. Based on this theory, we formulated a probabilistic proposition for each of the dimensions of distribution strategy: Proposition 1: Retailers with a higher number of stops per roundtrip are likely to have a higher increase in total distribution costs that occur with a given change in time access window pressure than retailers with a lower number of stops per roundtrip. Proposition 2: Retailers with a vehicle fleet with a higher capacity per vehicle are likely to have a higher increase in total distribution costs that occur with a given change in time access window pressure than retailers with a fleet of lower capacity per vehicle. Proposition 3: Retailers with longer stopping times are likely to have a higher increase in total distribution costs that occur with a given change in time access window pressure than retailers with shorter stopping times. Proposition 4: Retailers with longer distances from the distribution centre to their shops are likely to have a higher increase in total distribution costs that occur with a given change in time access window pressure than retailers with shorter distances from the distribution centre to their shops. Proposition 5: Retailers with less strict self-imposed time windows are likely to have a higher increase in total distribution costs that occur with a given change in time access window pressure than retailers with stricter self-imposed time windows.

7.2.2.4 Domain

As with the theory tested in Case Study 3, this theory applies to all large retailers that distribute goods from a distribution centre to shops that are at least partly located in shopping areas in cities in which time access windows could be installed.