The purpose of this study was to clarify the effect of increasing related items on the accuracy estimations of the item and the test. To achieve this purpose, the researcher developed a special multiple choice mathematic test consisting of 44 items. To identify independence within the test items, the researcher used Q3. The study was performed on a sample consisting of 997 ninth graders (male, female). The study findings indicated that increasing the related items led to biased estimations for higher discrimination coefficients, and to biased estimations down for both difficulty and reliability coefficients. The influence of increasing related items on the different estimations was less robust in tests containing high percentages of related items, specially in the case of high violation levels. This influence on different estimations was more robust in tests containing more independent items in the case of different violations.