methods of operating nonvolatile memory devices include testing a plurality of strings of nonvolatile memory cells in the memory device to identify at least one weak string therein having a higher probability of yielding erroneous read data error relative to other ones of the plurality of strings . an identity of the at least one weak string may be stored as weak column information . this weak column information may be used to facilitate error detection and correction operations . in particular , an error correction operation may be performed on a first plurality of bits of data read from the plurality of strings using an algorithm that modifies a weighting of the reliability of one or more data bits in the first plurality of bits of data based on the weak column information . more specifically , an algorithm may be used that interprets a bit of data read from the at least one weak string as having a relatively reduced reliability relative to other ones of the first plurality of data bits .