p(n + 1) = 4 [1 - b p(n)] p(n)
exhibits chaos unless p(1) is exactly an equilibrium point or a cycle.
Logistic models of the form
p(n + 1) = a [1 - b p(n)] p(n)
where a is close to 4 also exhibit chaos. It is interesting and somewhat difficult to determine how close a must be to 4 to have chaos.