Using Flexi to detect a trend in count and binary longitudinal data

Abstract

The Department of Conservation uses an aerial transect survey to monitor the number of Hector's dolphins around Banks Peninsula. Flights are made repeatedly along a set of 15 transects. Relative dolphin abundance can be measured by the number of dolphins counted in each transect, or by the presence or absence of dolphins in each transect. At times consecutive flights are only days apart and so consecutive measurements on the same transect are correlated. Flexi, Bayesian software for smoothing time series, can be used to detect a trend in count or binary longitudinal data. Flexi' s estimate of the trend can approximate the estimate from a generalised estimating equation model, or show the effect of measurement error.