Question 53 of the Spring 2003, Grade 11, Texas Assessment of Knowledge and Skills (TAKS) released Science test reads as follows:

                            Amino Acid Composition of Cytochrome c in Some Organisms
                      ____________________________________________________________

                      Amino Acid     Organism Q     Organism R     Organism S     Organism T
                      ____________________________________________________________

                      Alanine                 10%                 10%               10%               10%
                      Arginine                 4%                   4%                 4%                 4%
                      Aspartic acid           6%                   6%                 6%                 6%
                      Cysteine                 6%                   6%                 6%                 4%
                      Glutamic acid       12%                 12%                 8%                 8%
                      Glycine                   4%                   2%                 4%                 4%
                      Valine                     2%                   1%                 4%                 6%
                      ____________________________________________________________

            53   The table shows a comparison of some amino acids found in cytochrome c. The two organisms in the
                    table that are most closely related are ---

                    A     Q and T
                    B     R and S
                    C     Q and R
                    D     Q and S

      Out of the 187214 students who took the test, the response percentages for answers A, B, C, D, and no answer were, respectively, 6%, 9%, 73%, 11%, and 0%.

Scoring mistake?
      The smallest percentage change of amino acids from one organism to another that is consistent with the given information is a change of 2% from Organism S to Organism T, where the 2% is a change from Cysteine in Organism S to Valine in Organism T.  The next smallest change from one organism to another that is consistent with the given information is a change of 3% from Organism Q to Organism R, where 2% is a change from Glycine in Organism Q to unlisted amino acids in Organism R and 1% is a change from Valine in Organism Q to unlisted amino acids in Organism R.  A change of 3% could also occur from Organism S to Organism T, where 1% is a change from Cysteine in Organism S to Valine in Organism T, 1% is a change from Cysteine in Organism S to unlisted amino acids in Organism T, and 1% is a change from unlisted amino acids in Organism S to Valine in Organism T.  A change of 4% could also occur from Organism S to Organism T, where 2% is a change from Cysteine in Organism S to unlisted amino acids in Organism T and 2% is a change from unlisted amino acids in Organism S to Valine in Organism T.
      If correctness is based solely on the criterion "smallest percentage change of amino acids from one organism to another that is consistent with the given information", then the pair S and T is the correct answer, answer C is incorrect, and the Texas Education Agency made the mistakes of giving credit for the incorrect answer C and of not thowing out question 53.  In this case, the TEA wrongly increased the scores of those roughly (73%)(187214) = 136666 students who chose answer C and, with respect to scaled scores that result from throwing out question 53, wrongly decreased the scaled scores of those roughly (26%)(187214) = 48676 students who did not choose answer C.
      In choosing answer C, the TEA did not use as its sole criterion "smallest percentage change of amino acids from one organism to another that is consistent with the given information".  The TEA has not stated what other criteria it used or explained why students should have known that the TEA's criteria are correct.