Data on 30 items for upper case letters and 36 items for lower case letters, where each item was scored in one of two categories (wrong scored zero and correct scored one), were Rasch analysed to create two linear scales . The student sample was N=324 pre-primary and primary students (aged 5 to 9 years) in Perth, Western Australia. Twelve of the initial 30 items of Visual Discrimination of Upper Case Letters were deleted due to item misfit statistics leaving 18 items and five of the original 36 items for Visual Discrimination of Lower Case Letters were deleted leaving 31 items. The 18 item-scale and the 31 item-scale each had a good fit to the measurement model, were reliable (Person Separation Indices of 0.55 and 0.82 and Cronbach Alphas of 0.70 and 0.82), and were unidimensional, showing no statistically significant interaction on item difficulties along the scale. Items were ordered from easy to hard and student measures from low to high on the same scale, allowing the objective identification of alphabet letters that students found difficult to discriminate. Students who had poor visual discrimination skills of alphabet letters could also be identified objectively.
Available at: http://works.bepress.com/janet_richmond/4/