As William Dembski points out, drawing design inferences is already an essential and uncontroversial part of various scientific activities ranging from the detection of fabricated experimental data, to forensic science, cryptography, and even the search for extra-terrestrial intelligence (SETI). He identifies two criteria as necessary and sufficient for inferring intelligence or design: complexity and specification. Complexity ensures that the event in question is not so simple that it can readily be explained by chance. It is an essentially probabilistic concept. Specification ensures that the event in question exhibits the trademarks of intelligence. The notion of specification amounts to this: if, independently of the small probability of the event in question, we are somehow able to circumscribe and define it so as to render its reconstruction tractable, then we are justified in eliminating chance as the proper explanation for the event. Dembski calls such an event one of specified small probability.
One of Dembski's important contributions has been to render the notion of specification mathematically rigorous in a way that places design inferences on a solid foundation.
The mathematical analysis used to determine whether an event is one of specified small probability rests on empirical observations set in the context of the theoretical models used to study the domain (quantum-theoretic, molecular biological, developmental biological, cosmological, etc.) under investigation, but the design inference itself can be formulated as a valid deductive argument. One of its premises is a mathematical result that Dembski calls the law of small probability. That the design inference lends itself to this precision of expression is significant because it enables us to see that a rigorous approach to design inferences conforms to even the most restrictive theory of scientific explanation, the D-N model. In fact, even though the accounts of scientific explanation we considered were inadequate as universal theories, all three of them captured important intuitions. Furthermore, it is short work to see that rigorous design inferences satisfy the conditions imposed by all of them.
4truth.net
http://www.4truth.net/fourtruthpbscience.aspx?pageid=8589952949