In addition to the ct·ata on the dgricul tural clCtivities undertaken in the project area. the planner needs information on th~ potential i­ ties and constraints related to these activities in oraer to butld realistic targets and simulations. The main collstraints dre on ldnd an<t tabour availabilities; thus the follo.dnq data must be collected: Total land~ total arable an~ tota! irrigated areas; Family size and distribution according to age and sex of the farmer population; l"lanpower availability on the rural labour markets. On the basis of this information. the planners make a sinulation of the most likely development of the project area if no project were t:o oe undertaken.. The central estimation is made on the expected v:tl­ ue~ taken by the variables. ~.e. their average v~lues or the values expected from the past trendS• Parallel to this simu tatfon, di ffe..-ent scenarios a..-e built according to the most probabl e range of v;Hiation of the key variabfes. For that reason it is very useful for the plan­ ner to have. tQgether ~o~i th the estimated ~al ue of the var i db I e~ t ht:~ variance of the estimators, for both tiflle series and cross-sectional ~ata estimations. 6 -1 - This model is a linedr programming model of the agricultural sec­ tor of Tunisia. It is the resu1t of the co-operation between the Tunisian Ministry of A'Jriculture, the US Agency for International Development and FAO. The motlel is used for policy analysis. and its aim is to formalize the simultaneous interactions gov~rning the Tuni­ sian agricultural sector. The simulations made by this model heJp the planners to an~wer questions such as: ~ow does the pattern of pro­ ductivn respond to irrigation investments? Is existin•;:~ irrigation captta1 adequate in view of the domestic and foreign demand prospects? 
**Analysis**
The text appears to be focused on agricultural development and planning, with specific details about land use, labor availability, and irrigation investments. The model used is also specifically designed for policy analysis in the agricultural sector. This suggests that the text is related to economic development, agriculture, and policy-making.

**Category**
Agriculture, forestry and fishing, Economic development