電腦適性測驗 (簡稱CAT) 的試題安全性一般常用試題曝光率與測驗重疊率來評估，為了妥善控管此二指標，Chen和Lei (2005) 針對「固定長度」的CAT，提出SHT控管法，透過此方法，試題曝光率與測驗重疊率可以被妥善控管在一個安全範圍內，確保測驗的安全性。 本研究的主要目的是根據SHT的控管原理，發展一個新的曝光控管方法─SHTV，期能控管「變動長度」CAT的試題曝光率與測驗重疊率。研究結果顯示， SHTV確可在「變動長度」CAT中同時控管試題曝光率與測驗重疊率，雖然試題的安全性可透過嚴格控管測驗重疊率來提升，但測驗的效率會隨之明顯下降，受試者須接受更多的試題方能達到預先訂定的能力估計精確度。

Item exposure rate and test overlap rate are two indices commonly used to track item exposure in computerized adaptive tests (CATs). To control these two indices for fixed length CATs, Chen & Lei (2005) used the Sympson and Hetter procedure with test over­lap control (SHT). By implementing the SHT procedure, item exposure and test overlap can be controlled simultaneously. The purpose of this study is to propose an item exposure control method--SHTV to control item exposure and test overlap for variable length CATs. The SHTV procedure is an extension of the SHT procedure and designed to provide item exposure control at both the item and test levels for variable length CATs. Results indicated that item expo­sure rate and test overlap rate can be controlled simultaneously for variable length CATs by implementing the SHTV procedure. When a pre-specified maximum test overlap rate was stringent, test security was improved and efficiency of measurement decreased such that examinees needed to take more items to reach a pre-specified measurement precision.