At first it may seem a little odd , but bear with it it's quite fascinating. They took advantage, much as Ladurie did with Montaillou of extant medieval records to work out the network of social obligation. In this case they used 250 years worth of land tenancies (around 5000 documents) to work out the network of social obligation between lords and tenants, and its changes, between approximately 1260 and 1500, a period which encompassed both the black death and the hundred years' war. They also made use of supporting documents like wills and marriage contracts.
What is also interesting is the way that they used a record corpus which had been created for another project as input data for the Kevin Bacon style study, and along the way demonstrating the need for long term archiving and availability of data sets.
The important thing to realise is that medieval France was a society of laws and contracts rather than the Hollywood view of anarchy, rape, pillage and general despoilation. Sure there was a lot of that during the hundred years war, but outside of that, there was a widespread use of written agreements, which were drawn up by a notary and lodged appropriately.
The other useful thing is that these documents were written to a formula. Notaries processed hundreds of them in their careers and they wrote them all in more or less the same way. This means that even though they're written on calfskin in spidery late medieval script they can be codified in a database and treated as structured information, and analysed on the basis of network theory by being able to plot the closeness of particular relationships between individuals.
So what did they find?
Nothing startling. It confirmed the previous suppositions of historians. Slight letdown, but still very interesting as much of history is based on textual records of the seigneurial (landowning) class and the doings of senior ecclesiastics, for the simple reason that they were part of the literate universe, and the peasants who made up 85-90% of the population were not. That's why we have tales of courtly love but not 'swine herding for fun and profit'.
broadly they found that the seigneurial class contracted during the hundred years war, relationships became more linear with a number of richer more successful peasants buying up smaller and abandoned farms, and that in the course of the hundred years war some peasants developed wider social networks themselves, due to them taking over a number of tenancies and effectively becoming rentiers.
We also see the seigneurial class renewing itself over time, and also people moving in from outside to take over vacant tenancies.
As I said nothing remarkable However the technique is interesting and it might be interesting to run the same sort of analysis on town rent rolls etc to try and get a more accurate gauge of the impacts of the black death etc.