One of the more difficult aspects of cyclical analysis in my opinion is correctly dealing with price wave expansion or contraction in a timely manner. If one waits long enough the difficulty will usually resolve itself in an additional cycle. However if the price wave in question is of intermediate length, one usually does not have the luxury of waiting. The S&P 500 in currently facing such a situation. It is somewhat unclear as to whether the 20 and 10 week price waves have expanded or contracted. Other analysts have postulated that the 20 week wave has expanded. It appears from a spectral viewpoint that the waves may have contracted, particularly the 10 week price wave.
Below is a daily chart of the ES futures covering approximately 9 months. The two price waves shown at the bottom of the chart are the 20 day (blue and white) and the 10 week (yellow). I superimposed the 10 week filter output onto the 20 day filter output. For the past several months the two waves have exhibited a textbook simple harmonic relationship and very closely synchronized troughs. The two most recent oscillations of the 10 week show a moderate decrease in period, particularly the most recent one which is one day shorter than the shortest 10 week oscillation over the past two years.
When the period of dominant price waves starts decreasing and the amplitude of the shorter waves starts increasing, the risk of a price inversion (i.e. price drops below the prior cyclical low while the the price wave is cycling up) is greatly increased. A price inversion of a dominant intermediate wave is a clear sign of a change in the trend underlying such wave. There have been no price inversions on the 10 week wave in the S&P 500 since the prior 4 year low, well over two years. The index is within shouting distance of the 3/11/15 low close. A daily close this week below that low may be more than from which the index can immediately recover. Time will tell.