Symmetry The shoulders should bottom near the same price, be nearly the same distance from the head, and look similar to their mirror opposite
Volume trend Usually higher on the left side of the pattern. Trends downward 65% of the time. The link to the left gives an example and this link discusses performance.
Neckline Joins the highest armpits.
Confirmation The pattern confirms as a valid one when price closes above a down-sloping trendline or above the right armpit when the neckline slopes upward.