背景與目的：本研究利用遠紅外線雷射測量儀合併紙張校正法（雷射儀紙張測量法）來測量功能性腿長差異。實驗目的為驗證此測量法之信度與效度。方法：利用遠紅外線雷射測量儀，臨床可直接使用於評估功能性腿長差異。本研究信度研究部分包含驗證同一施測者重覆施測與不同施測者間量測之信度。效度部分包含利用模擬功能性腿長差異來驗證建構效度，及篩選出明顯有功能性腿長差異的受測者來驗證同時效度。結果：雷射儀紙張測量法具有極高的信度，共有18位受測者參與此部分研究，施測者內之級內相關係數(ICC)為0.984；施測者間ICC=0.968；及具有很小的測量差異，施測者A兩次測量間的平均差異為0.09 cm，施測者A兩次測量(A1、A2)與B施測者之間的測量平均差異分別為0.21與0.30 cm。而測量值的標準誤亦小於0.065 cm，顯示測量相當精準。建構效度部分為17位受測者隨機抽選兩種模擬高度差，與雷射儀紙張測量法之測量值比較，結果顯示有高度的相關性，皮爾遜相關係數為0.991，表示有極高的建構效度以及很小的測量差異（兩者平均差異為0.36 cm）。同時效度部分共有7位受測者，雷射儀紙張測量與X光片上直接測量的結果（兩側股骨頭、髂骨脊頂端高度差）也呈現高度相關（r分別為0.921與0.960）。結論：利用雷射儀紙張測量法來測量功能性腿長差異具有高度的信度和效度。當受測者沒有骨盆畸形的病史，同時腸骨前上脊可以很容易觸摸到時，我們建議利用雷射儀測量法來測量功能性下肢長度差異，並利用紙張校正法來加以定量。雷射儀紙張測量法在臨床使用上具有快速、簡便且能精準的量化功能性下肢長度差異，值得臨床相關工作者推廣使用。

Background and Purposes: This study as to examine the reliability and validity of clinical measurement of functional leg-length discrepancy (FLLD) by using the far infrared laser and paper correction (LPC) method. Methods: The laser beam, unlike ordinary light, consists of parallel ayes that propagate with a high degree of order approximating the same phase and same direction. These properties, referred to as temporal and spatial coherence, minimize divergence and focus the energy so that it is concentrated in one area. The laser beams ere used to point out the landmarks and to assess the FLLD in this study. The intra-rater and inter-rater reliability ere examined by repeated measurement of the LPC by Rater A, and to raters (A, B). The construct validity vas examined by to randomly selected simulated differences of FLLD and LPC measured in each subject. The concurrent validity was determined by examining the differences between to femoral heads (DFH)/iliac crests (DIC) on X-ray and LPC measures. Results: The intra-class correlation coefficients for the intra-rater and inter-rater reliabilities were 0.984 and 0.968, respectively. The standard errors of measurement were less than 0.065 cm. showing that the LPC method as a precision measurement. The Pearson correlation coefficients for the construct and concurrent validities were 0.991 and 0.921 with DFH, and 0.960 with DIC, respectively. Conclusions: The LPC method is highly reliable and valid for measuring FLLD. When there is no history of pelvic deformity and the iliac crests can be easily palpated, we recommend using this method to measure the FLLD. The LPC method provides quick assessment and convenience and makes it easy to quantify the FLLD in either a clinical or research setting. Thus, it is recommended.