In precision measurements of neutrino oscillation parameters and in the search for theta(13), it becomes important to study small effects which may alter the precision measurements or mimic a theta(13) signal. Here, I give an introduction to a common framework in which many of the possible small effects - such as neutrino wave packet decoherence, neutrino quantum decoherence, and neutrino decay - can be studied. This framework is based on the introduction of damping factors on the probability level of the neutrino oscillation formulas.