Lagging indicator

A measure that turns after the thing it describes. The label is used in two settings that share the idea and share nothing else. In economics it names a statistic that historically changes direction after the wider economy has, the unemployment rate and average earnings being the standard examples, since employers cut hours and pay well after demand has fallen. In chart work it names any calculation built from prices that have already printed, of which a moving average is the plainest case.

The delay is arithmetic rather than a flaw in the design. An average of a window of past prices cannot move until a new price enters the window, and the older prices inside it hold the value back, so a longer window produces a smoother line and a later turn. That trade is the entire choice being made: smoothing is bought with time, and there is no window length that supplies both. The same logic governs an economic series, where the delay comes from collection and revision as well as from the behaviour being measured.

Two things are commonly misread. The first is that lagging is a criticism: a confirmation that arrives late is still a confirmation, and a great deal of chart work is deliberately built on late but stable readings rather than early but noisy ones. The second is the division itself. Every technical indicator is computed from prices that have already traded, so on a strict reading none of them leads anything, and practitioners disagree about whether the leading label describes a property of the calculation or only a habit of interpreting it. What is not disputed is that the lag of a smoothed series can be measured, while the lead of an oscillator cannot.