  Searches for known waveforms in gravitational wave detector data are often
done using matched filtering. When used on real instrumental data, matched
filtering often does not perform as well as might be expected, because
non-stationary and non-Gaussian detector noise produces large spurious filter
outputs (events). This paper describes a chi-squared time-frequency test which
is one way to discriminate such spurious events from the events that would be
produced by genuine signals. The method works well only for broad-band signals.
The case where the filter template does not exactly match the signal waveform
is also considered, and upper bounds are found for the expected value of
chi-squared.
