变点分析法(change point analysis,CPA)近些年才引入心理与教育测量学,相较于传统方法,CPA不仅可以侦查异常作答被试,还能自动精确地定位变点位置,高效清洗作答数据。其原理在于:判断作答序列中是否存在可将该序列划分为具有不同统计...变点分析法(change point analysis,CPA)近些年才引入心理与教育测量学,相较于传统方法,CPA不仅可以侦查异常作答被试,还能自动精确地定位变点位置,高效清洗作答数据。其原理在于:判断作答序列中是否存在可将该序列划分为具有不同统计学属性两部分的点(即变点),并且需使用被试拟合统计量(person-fit statistic,PFS)来量化两个子序列之间的差异。未来可将单变点分析拓展至多变点,结合反应时等信息,构建非参数化指标以及将现有指标拓展至多级计分或多维测验,以提高CPA的适用广度及效力。展开更多
The cumulative sum （CUSUM） algorithm is proposed to detect the selfish behavior of a node in a wireless ad hoc network. By tracing the statistics characteristic of the backoff time between successful transmissions, ...The cumulative sum （CUSUM） algorithm is proposed to detect the selfish behavior of a node in a wireless ad hoc network. By tracing the statistics characteristic of the backoff time between successful transmissions, a wireless node can distinguish if there is a selfish behavior in the wireless network. The detection efficiency is validated using a Qualnet simulator. An IEEE 802.11 wireless ad hoc network with 20 senders and 20 receivers spreading out randomly in a given area is evaluated. The well-behaved senders use minimum contention window size of 32 and maximum con- tention window size of I 024, and the selfish nodes are assumed not to use the binary exponential strategy for which the contention window sizes are both fixed as 16. The transmission radius of all nodes is 250 m. Two scenarios are investigated： a single-hop network with nodes spreading out in 100 m^100 m, and all the nodes are in the range of each other; and a multi-hop network with nodes spreading out in 1 000 m~ 1 000 m. The node can monitor the backoff time from all the other nodes and run the detection algorithms over those samples. It is noted that the threshold can significantly affect the detection time and the detection accuracy. For a given threshold of 0.3 s, the false alarm rates and the missed alarm rates are less than 5%. The detection delay is less than 1.0 s. The simulation results show that the algorithm has short detection time and high detection accuracy.展开更多
文摘变点分析法(change point analysis,CPA)近些年才引入心理与教育测量学,相较于传统方法,CPA不仅可以侦查异常作答被试,还能自动精确地定位变点位置,高效清洗作答数据。其原理在于:判断作答序列中是否存在可将该序列划分为具有不同统计学属性两部分的点(即变点),并且需使用被试拟合统计量(person-fit statistic,PFS)来量化两个子序列之间的差异。未来可将单变点分析拓展至多变点,结合反应时等信息,构建非参数化指标以及将现有指标拓展至多级计分或多维测验,以提高CPA的适用广度及效力。
基金Supported by National Natural Science Foundation of China (No. 60702038)National High Technology Research and Development Program of China ("863"Program, No. 2007AA01Z220)Cultivation Fund of Innovation Project,Ministry of Education of China (No. 708024)
文摘The cumulative sum （CUSUM） algorithm is proposed to detect the selfish behavior of a node in a wireless ad hoc network. By tracing the statistics characteristic of the backoff time between successful transmissions, a wireless node can distinguish if there is a selfish behavior in the wireless network. The detection efficiency is validated using a Qualnet simulator. An IEEE 802.11 wireless ad hoc network with 20 senders and 20 receivers spreading out randomly in a given area is evaluated. The well-behaved senders use minimum contention window size of 32 and maximum con- tention window size of I 024, and the selfish nodes are assumed not to use the binary exponential strategy for which the contention window sizes are both fixed as 16. The transmission radius of all nodes is 250 m. Two scenarios are investigated： a single-hop network with nodes spreading out in 100 m^100 m, and all the nodes are in the range of each other; and a multi-hop network with nodes spreading out in 1 000 m~ 1 000 m. The node can monitor the backoff time from all the other nodes and run the detection algorithms over those samples. It is noted that the threshold can significantly affect the detection time and the detection accuracy. For a given threshold of 0.3 s, the false alarm rates and the missed alarm rates are less than 5%. The detection delay is less than 1.0 s. The simulation results show that the algorithm has short detection time and high detection accuracy.
