Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành y học dành cho các bạn tham khảo đề tài: Evaluation of internal reliability in the presence of inconsistent responses | Fong et al. Health and Quality of Life Outcomes 2010 8 27 http content 8 1 27 HEALTH AND QUALITY of life outcomes RESEARCH Open Access Evaluation of internal reliability in the presence of inconsistent responses Daniel YT Fong 1 S Y Ho2 T H Lam2 Abstract Background We aimed to assess the impact of inconsistent responses on the internal reliability of a multi-item scale by developing a procedure to adjust Cronbach s alpha. Methods A procedure for adjusting Cronbach s alpha when there are inconsistent responses was developed and used to assess the impact of inconsistent responses on internal reliability by evaluating the standard Chinese 12-item Short Form Health Survey in adolescents. Results Contrary to common belief random responses may inflate Cronbach s alpha when their mean differ from that of the true responses. Fixed responses inflate Cronbach s alpha except in scales with both positive and negative polarity items. In general the bias in Cronbach s alpha due to inconsistent responses may change from negative to positive with an increasing number of items in a scale but the effect of additional items beyond around 10 becomes small. The number of response categories does not have much influence on the impact of inconsistent responses. Conclusions Cronbach s alpha can be biased when there are inconsistent responses and an adjustment is recommended for better assessment of the internal reliability of a multi-item scale. Background Internal reliability is an attribute of a multi-item scale that refers to the extent to which items in the scale are related it is very often evaluated to assess the reliability of patient-reported outcomes PROs . The most common measure of internal reliability reported in psychometric studies of PROs is Cronbach s alpha 1 but unfortunately it can be biased by the presence of inconsistent responses. Inconsistent responding occurs when respondents complete a questionnaire without comprehending the items typically in .
