In the literature, the number one quantitative evidence of chaos is a positive maximum Lyapunov exponent (i.e. Filip Larsen's "sensitivity to initial conditions").
Stephen Strogatz [1] has perhaps the most popular known criteria:
1) It must be a deterministic system
2) Solutions are irregular (not periodic or steady state)
3) Sensitivity to initial conditions
All you can really demonstrate quantitatively, given 1), is 3) with a positive maximum Lyapunov exponent. 2) is a rather subjective condition, and sometimes systems don't appear irregular, but actually are.
jump between attractions?
If the system is deterministic, there will be no jumping between attractors. There are cases where there is what Karl Firston calls a "complex attractor" and the trajectory will move around different parts of the attractor, giving the appearance that the underlying attractor is changing, but since it's a deterministic system with fixed parameters, the underlying attractor cannot change, and trajectories will always approach the attractor who's basin they are in. Anyway, you can have chaos in a system with just one chaotic attractor.
[1] http://books.google.ca/books/about/Nonlinear_Dynamics_and_Chaos.html?id=FIYHiBLWCJMC&redir_esc=y