and an overvote in the analyses and reports mentioned above. Mochán's article reports almost three times as many undervotes as overvotes in the aggregated totals. Mochán notes that "it is quite probable that many of the inconsistencies has [sic] its origin in errors made without malice", listing several possible such errors (some mentioned explicitly above). Mochán strongly stresses that in his opinion these and other explanations considered are "not enough to explain the magnitude of errors." Mochán's analyses are about the PREP numbers. The PREP totals are ignored when the official count begins, and do not have any legal validity for the purposes of deciding the election. On the other hand, the existence of overvotes and of undervotes is one of the grounds for requesting that an electoral packet be opened and recounted. Mochán notes that the official totals does not include the information on leftover blank ballots, so that a verification of undervotes and overvotes in the case of adding up errors is impossible. The Center for Economic and Policy Research (CEPR) reported that "61,192 of 126,139 ballot boxes contained 'adding up' errors. Election workers received a fixed and recorded number of blank ballots for each ballot box, and were instructed to keep track of them. Yet for nearly half of all ballot boxes, the total votes plus leftover blank ballots did not add up to the number of ballots received." Pliego Carrasco compared the size and type of the errors in the different polling places, sorted according to who won the polling place. For example, for polling places in which the number of ballots issued to the polling place is different from the number of votes tallied plus the number of leftover ballots, he gives the table below. The FCH column gives the number of polling places where Calderón received the most votes that exhibited that type of error, while the AMLO column shows the number where López Obrador received the most votes. Undervotes refers to the case where the number of votes tallied plus the number of leftover ballots is less than the number of blank ballots allocated to the polling place, while Overvotes is the case where the number of allocated blank ballots is less than the votes tallied plus leftover ballots. The numbers are also taken from the PREP. Pliego Carrasco notes that both the absolute and relative numbers are very close for both candidates.