How Does "Sentence Structure and Vocabulary" Function as a Scoring Criterion Alongside Other Criteria in Writing Assessment?

Several studies have evaluated sentence structure and vocabulary (SSV) as a scoring criterion in assessing writing, but no consensus on its functionality has been reached. The present study presents evidence that this scoring criterion may not be appropriate in writing assessment. Scripts by 182 ESL students at two language centers were analyzed with the Rasch partial credit model. Although other scoring criteria functioned satisfactorily, SSV scores did not fit the Rasch model, and analysis of residuals showed SSV scoring on most test prompts loaded on a benign secondary dimension. The study proposes that a lexico-grammatical scoring criterion has potentially conflicting properties, and therefore recommends considering separate vocabulary and grammar criteria in writing assessment.