14. The method of claim 12 , comprising determining the parameters of the probabilistic model of individuals' responses, including both features describing the individuals and the messages, from observations of past individuals' activity.
14. The method of claim 12 , comprising determining the parameters of the probabilistic model of individuals' responses, including both features describing the individuals and the messages, from observations of past individuals' activity. 16. The method of claim 14 , comprising the probabilistic model of individuals' responses, wherein the features describing the messages RC D (c) are updated per each observation of either positive or negative response from an individual to a distributed message according to Δ ⁢ ⁢ RC D ⁡ ( c ) = 1 E - ( 1 - PI X ⁡ ( D ) ) ⁢ ∂ P D ⁡ ( c )  ∂ P  ⁢ lr , where ∂P D (c) is a vector with respect to category index c, defined as ∂ P D ⁡ ( c ) = ∑ Y ∈ A ⁡ ( D ) ⁢ VI X Y ⁡ ( c ) 1 - RC D ⁡ ( c ) ⁢ VI X Y ⁡ ( c ) , |∂P| means the norm of that vector in conventional sense, E=1 for positive and E=0 for negative response from individual X to message D, and lr is an adjustable learning rate.