of monitoring activity over time, and the ARIJ data are highly correlated to those collected by OCHA for the years in which both sources are available (i.e. since 2006), which should add confidence to the consistency of the data over time and across sources.<sup>15</sup> We have data on most barriers, including permanent check-points, partial checkpoints, roadblocks, earth mounds, road gates, agricultural and barrier gates.<sup>16</sup> Checkpoints are infrastructures which inhibit vehicular and pedestrian traffic and are manned by Israeli security personnel, which usually check the documentation of persons crossing the checkpoint and conduct searches on their vehicles and belongings. Unlike permanent checkpoints, partial checkpoints are only occasionally manned. Earth mounds are mounds of rubble, dirt and/or rocks put in place by the Israeli army (IDF) to prevent vehicular movement along a road (usually secondary) or a track. Earth mounds are often removed or circumvented and then re-built and/or enlarged (OCHA, 2010). Roadblocks are constructed from one or more concrete blocks of about one cubic meter. Similarly to earth mounds, they are also used to prevent vehicle access to land or roads often at the entrance of villages, towns and cities. Agricultural gates and barrier gates are metal gates which provide the only access through the West Bank wall to the so-called “seam zone”. This is an area comprised between the internationally recognized border between the West Bank and Israel (the “green line” in Figure 2) and the wall (the solid black line in Figure 2), which is almost entirely constructed inside the West Bank territory and whose total length upon completion will be 760 km. The “seam zone” comprises around 8.5% of the West Bank and includes a number of villages and several hectares of agricultural land, which have been cut off from the rest of the West Bank by the wall. These gates usually require permission to be crossed and have specific opening times which may vary over time. Agricultural gates are used mainly by the owners of the land in the “seam zone” who live on the other side of the wall, while barrier gates are used by the residents of the villages in the “seam zone” to access the rest of the West Bank and by lorries transporting goods from the West Bank into the “seam zone”. The last type of barrier in our dataset is road gates. These are

> measurement error, which should however be minimized by the fact that the vast majority of the barriers in every year have been present since the beginning of that year.

> 15 The slight differences in the barriers’ data between OCHA and ARIJ refer mainly to the non check-point barriers and are likely to be mainly due to the different timing of the monitoring activity.

> 16 Data on other types of barriers, including road barriers, trenches and earth walls is not consistently available over the period of analysis due to the difficulty in monitoring such barriers and is therefore excluded from the analysis. While this may generate some omitted variable bias, its size should be relatively small as these represent minor obstructions and their placement may reflect to some extent that of the other barriers.

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