However, the Orme (2001) and Wooldridge (2005) estimators can be applied to unbalanced panels if it assumed that sample dropout is ignorable - the unobservable determinants of attrition are not correlated with the unobservables determining SA receipt. The main arguments against balancing are that its enforcement may introduce potentially nonrepresentative samples (because a specific type of sample drop-out is being imposed by the researcher), reduce sample size, and coverage in calendar time. To derive most of their results, Cappellari and Jenkins (2008a) use an unbalanced panel in which the majority of the benefit histories begin in 1991 but some start in later years (the maximum sequence length is 15 years). However, they also examine the sensitivity of their findings by re-running their basic DREP model on (i) an unbalanced panel in which all individuals’ histories begin in 1991 and (ii) a balanced panel in which every individual contributes 15 years of data (which reduces sample size substantially). The state dependence is [also] similar” (2008: 54).