549. In situations as described in paragraphs 540–542, it is common for the electoral legal frameworks (or the case law) to set out assumptions that define when the annulment of the vote at a particular or several polling stations should be considered to be a reason to believe that the irregularities involved affect the overall election result, in which case a new election must be called. These include if the nullity of the votes affects more than half the polling stations, if the nullities in the voting affect more than half the votes cast or if they represent one-third of the valid votes cast nationally. In some countries the nullity of the votes at 20 per cent of the polling stations is the threshold established for annulment of the whole election. ii) For reasons of ineligibility of a candidate or slate of candidates 550. A large number of electoral laws provide that there is ground for the annulment of an election if the candidate or the persons on a slate of candidates do not meet the eligibility requirements, or the candidate concerned has made fraudulent representations in this regard. Even in those countries that do not provide that this is a ground for annulling an election, when it subsequently turns out that a candidate elected is ineligible, the only possible measure is revocation of the declaration or certification. iii) When the election is not accompanied by the necessary guarantees 551. Several electoral legal frameworks establish as grounds for annulment of the election that there have been sufficient acts of violence or coercion to alter the result, and thus that the election has been held without the necessary guarantees (e.g. Bolivia, Panama); that there has been widespread distortion of the vote count due to error, fraud or violence (e.g. Paraguay); that infractions have made it impossible to establish the genuine will of the voters (e.g. Russia); that corrupt or illegal practices for the purpose of promoting or procuring the election of any person have been so extensive that they may reasonably have affected the result (e.g. the UK); or that there have been actions that have vitiated the election in that they influence the general results (e.g. Uruguay). 552. The above instances involve various concepts, such as ‘guarantees required’, ‘acts that vitiated the election’, ‘widespread distortion of the vote counts’ or ‘extensively prevailed’, which do not give the EDRB complete discretion in terms of the power to decide freely and with care but instead require it to decide in a reasoned way on the technical application of indeterminate legal concepts and their adaptation for the purpose in hand. For this reason, in addition to being broadly bound by precedent, the 179 7. Basic elements of EDR systems i) As a consequence of the annulment of the vote at various polling stations