Models and data are almost not separable. Methodological concepts can only be put to work if the necessary data are available. Equally, results obtained with a model mirror the quality of the underlying data. The CAPRI modelling team consequently invested considerable resources to build up a data base suitable for the purposes of the project. From the beginning, the idea was to create wherever possible sustainable links to well-established statistical data and to develop algorithms which can be applied across regions and time, so that an automated update of the different pieces of the CAPRI data base could be performed as far as possible.

The main guidelines for the different pieces of the data base are:

• Wherever possible link to harmonised, well documented, official and generally available data sources to ensure wide-spread acceptance of the data and their sustainability.
• Completeness over time and space. As far as official data sources comprise gaps, suitable algorithms were developed and applied to fill these.
• Consistency between the different data (closed market balances, perfect aggregation from lower to higher regional level etc.)
• Consistent link between ‘economic’ data as prices and revenues and ‘physical data’ as farm and market balances, crop rotations, herd sizes, yields and input demand.

According to the different regional layers interlinked in the modelling system, data at Member State level (in terms of modelling) currently EU28 plus Norway, Turkey and Western Balkan countries need to fit to data at regional level administrative units at the so-called NUTS 2 level, about 300 European regions and data at global level, currently 44 “non supply-model-regions. A further layer consists of georeferenced information at the level of clusters of 1×1 km grid cells which serves as input in the spatial down-scaling part of CAPRI. This data base is discussed along with the methodology and not in the current chapter. As it would be impossible to ensure consistency across all regional layers simultaneously, the process of building up the data base is split in several parts:

• Building up the data base at national or Member State level. It integrates the EAA (valued output and input use) with market and farm data, with areas and herd sizes and a herd flow model for young animals (Section 3.2).
• Building up the data base at regional or NUTS 2 level , which takes the national data basically as given (for purposes of data consistency), and includes the allocation of inputs across activities and regions as well as consistent acreages, herd sizes and yields at regional level (Section 3.3).
• The input allocation step is a key step in the establishment of the database. It allows the calculation of regional and activity specific economic indicators such as revenues, costs and gross margins per hectare or head and is covered in a separate Section 3.4.
• Building up the global data base, which includes supply utilisation accounts for the other regions in the market model, bilateral trade flows, as well as data on trade policies (Most Favourite Nation Tariffs, Preferential Agreements, Tariff Rate quotas, export subsidies) (Section 3.5).
• Given the extent of public intervention in the agricultural sector, policy data complete the database. They are partly supply oriented CAP instruments like premiums and quotas and partly data on trade policies (Most Favourite Nation Tariffs, Preferential Agreements, Tariff Rate quotas, export subsidies) plus data domestic market support instruments (market interventions, subsidies to consumption), see Section 3.6.

The basic principle of the CAPRI data base is that of the ‘Activity Based Table of Accounts’ which roots in the combination of a physical and valued input/output table including market balances, activity levels (acreages and herd sizes) and the EAA.