I have mentioned many times over the years that my view on the markets is that they are essentially random. We cannot tell what will happen tomorrow or the next few days with any degree of certainty. However for those interested in something a little more scientific with a probability more certain than the toss of a coin; you need to think in terms of conditional probabilities.
Look for circumstances whereby certain conditions are present and make sure the data sample is representative and large enough to cater for a very wide range of circumstances. In the chart below John Hussman has put together some research that resonates with where I am holding in my market world view.