Data obtained from accelerated life testing （ALT） when there are two or more failure modes, which is commonly referred to as competing failure modes, are often incomplete. The incompleteness is mainly due to censori...Data obtained from accelerated life testing （ALT） when there are two or more failure modes, which is commonly referred to as competing failure modes, are often incomplete. The incompleteness is mainly due to censoring, as well as masking which might be the case that the failure time is observed, but its corresponding failure mode is not identified. Because the identification of the failure mode may be expensive, or very difficult to investigate due to lack of appropriate diagnostics. A method is proposed for analyzing incomplete data of constant stress ALT with competing failure modes. It is assumed that failure modes have s-independent latent lifetimes and the log lifetime of each failure mode can be written as a linear function of stress. The parameters of the model are estimated by using the expectation maximum （EM） algorithm with incomplete data. Simulation studies are performed to check＇model validity and investigate the properties of estimates. For further validation, the method is also illustrated by an example, which shows the process of analyze incomplete data from ALT of some insulation system. Because of considering the incompleteness of data in modeling and making use of the EM algorithm in estimating, the method becomes more flexible in ALT analysis.展开更多
<Abstract>AIM: To report our experience with computed tomog- raphy colonography (CTC) systematically performed in subjects with positive faecal occult blood test (FOBT) and an incomplete colonoscopy in the setti...<Abstract>AIM: To report our experience with computed tomog- raphy colonography (CTC) systematically performed in subjects with positive faecal occult blood test (FOBT) and an incomplete colonoscopy in the setting of a population-based screening for colorectal cancer (CRC). METHODS: From April 2006 to April 2007, 43 290 indi- viduals (age range 50-70) who adhered to the regional screening program for the prevention of CRC under-went immunochemical FOBT. FOBT was positive in 1882 subjects (4.3%). 1463 (77.7%) of these subjects underwent colonoscopy, 903 performed in a single center. Of 903 colonoscopies 65 (7.2%) were incom- plete. Forty-two of these subjects underwent CTC. CTC was performed with a 16-MDCT scanner after standard bowel prep (polyethyleneglycole) in both supine and prone position. Subjects whose CTC showed polyps or masses were referred to the endoscopist for repeat colonoscopy under sedation or underwent surgery. Per-lesion and per-segment positive predictive values (PPV) were calculated. RESULTS: Twenty-one (50%) of 42 CTCs showed pol-yps or masses. Fifty-five of these subjects underwent a repeat colonoscopy, whereas 2 subjects underwentsurgery for colonic masses of indeterminate nature. Four subjects refused further examinations. CTC cor- rectly identified 2 colonic masses and 20 polyps. PPV for masses or polyps greater than 9 mm was of 87.5%. Per-lesion and per-segment PPV were, respectively, 83.3% and 83.3% for polyps greater or equal to 10 mm, and 77.8% and 85.7% for polyps of 6-9 mm. CONCLUSION: In the context of a screening program for CRC based on FOBT, CTC shows high per-segment and per-lesion PPV for colonic masses and polyps greater than 9 mm. Therefore, CTC has the potential to become a useful technique for evaluation of the non visualized part of the colon after incomplete colonos-copy.展开更多
In this paper, we have discussed a random censoring test with incomplete information, and proved that the maximum likelihood estimator(MLE) of the parameter based on the randomly censored data with incomplete informat...In this paper, we have discussed a random censoring test with incomplete information, and proved that the maximum likelihood estimator(MLE) of the parameter based on the randomly censored data with incomplete information in the case of the exponential distribution has the strong consistency.展开更多
基金supported by Sustentation Program of National Ministries and Commissions of China (Grant No. 203020102)
文摘Data obtained from accelerated life testing （ALT） when there are two or more failure modes, which is commonly referred to as competing failure modes, are often incomplete. The incompleteness is mainly due to censoring, as well as masking which might be the case that the failure time is observed, but its corresponding failure mode is not identified. Because the identification of the failure mode may be expensive, or very difficult to investigate due to lack of appropriate diagnostics. A method is proposed for analyzing incomplete data of constant stress ALT with competing failure modes. It is assumed that failure modes have s-independent latent lifetimes and the log lifetime of each failure mode can be written as a linear function of stress. The parameters of the model are estimated by using the expectation maximum （EM） algorithm with incomplete data. Simulation studies are performed to check＇model validity and investigate the properties of estimates. For further validation, the method is also illustrated by an example, which shows the process of analyze incomplete data from ALT of some insulation system. Because of considering the incompleteness of data in modeling and making use of the EM algorithm in estimating, the method becomes more flexible in ALT analysis.
文摘<Abstract>AIM: To report our experience with computed tomog- raphy colonography (CTC) systematically performed in subjects with positive faecal occult blood test (FOBT) and an incomplete colonoscopy in the setting of a population-based screening for colorectal cancer (CRC). METHODS: From April 2006 to April 2007, 43 290 indi- viduals (age range 50-70) who adhered to the regional screening program for the prevention of CRC under-went immunochemical FOBT. FOBT was positive in 1882 subjects (4.3%). 1463 (77.7%) of these subjects underwent colonoscopy, 903 performed in a single center. Of 903 colonoscopies 65 (7.2%) were incom- plete. Forty-two of these subjects underwent CTC. CTC was performed with a 16-MDCT scanner after standard bowel prep (polyethyleneglycole) in both supine and prone position. Subjects whose CTC showed polyps or masses were referred to the endoscopist for repeat colonoscopy under sedation or underwent surgery. Per-lesion and per-segment positive predictive values (PPV) were calculated. RESULTS: Twenty-one (50%) of 42 CTCs showed pol-yps or masses. Fifty-five of these subjects underwent a repeat colonoscopy, whereas 2 subjects underwentsurgery for colonic masses of indeterminate nature. Four subjects refused further examinations. CTC cor- rectly identified 2 colonic masses and 20 polyps. PPV for masses or polyps greater than 9 mm was of 87.5%. Per-lesion and per-segment PPV were, respectively, 83.3% and 83.3% for polyps greater or equal to 10 mm, and 77.8% and 85.7% for polyps of 6-9 mm. CONCLUSION: In the context of a screening program for CRC based on FOBT, CTC shows high per-segment and per-lesion PPV for colonic masses and polyps greater than 9 mm. Therefore, CTC has the potential to become a useful technique for evaluation of the non visualized part of the colon after incomplete colonos-copy.
文摘In this paper, we have discussed a random censoring test with incomplete information, and proved that the maximum likelihood estimator(MLE) of the parameter based on the randomly censored data with incomplete information in the case of the exponential distribution has the strong consistency.
