Uniformly Balanced Repeated Measurements Designs in the Presence of Subject Dropout

Low, Lewis and Prescott (1999) showed that a crossover design based on a Williams Latin square of order 4 can suffer substantial loss of efficiency if some observations in the final period are unavailable. Indeed, if all observations are missing, the design becomes disconnected. We derive the information matrix for the direct effects of a Uniformly Balanced Repeated Measurements Design (UBRMD) in t periods when subjects may drop out before the end of the study and examine the maximum loss of information. The special case of loss of observations in the final period only is examined in detail. In particular we show that a UBRMD in t>= 5 periods remains connected when some or all observations in the final period are unavailable.