İki İşlem Üç Periyot Dual Dengeli Çapraz Tasarımların Nesne Düşüşlerine Sağlamlığının Değerlendirilmesi

Öz

Çapraz tasarımlar, çeşitli işlemlerin karşılaştırılması amacıyla klinik ve medikal alanlarda sıkça kullanılan popüler tasarımlardır. Bu tasarımlarda, her bir deney birimine her bir farklı zaman periyodunda bir işlem uygulanır ve her periyot sonunda deneğin yanıtı alınır. Çapraz tasarımlarda denekler (nesneler)  çalışmayı işlem sırasını tamamlamadan bıraktığında yanlı sonuçlara, deneyin istatistiksel gücünde azalmaya, hatta tasarımın temel işlem karşılaştırmalarının yapılamadığı bağlantısız tasarıma dönüşmesi gibi oldukça ciddi sorunlara neden olabilir. Bu çalışmada, ilgilenilen işlem karşılaştırmalarının denek içi ölçümlerden elde edilen farklar kullanılarak tahminini mümkün kılan iki işlem üç periyot dual dengeli tasarımların son periyot nesne düşüşleri durumunda sağlamlıkları, A optimallik kriteri kullanılarak elde edilen performans ölçüleri ve bağlantısız tasarım üretme olasılıkları incelenerek değerlendirilmiştir.

Anahtar Kelimeler

• Çapraz tasarımlar
• Nesne düşüşü
• Sağlamlık
• Bağlantısız tasarımlar
• Dual dengeli tasarımlar

Assessing the Robustness of Two Treatments Three Periods Dual Balanced Crossover Designs to Subject Dropout

Öz

Crossover designs are very popular designs which are frequently used in clinical and medical research to compare various treatments. In these designs, one treatment is given to each subject for each different time period and response of each subject is taken at the end of each period. When subjects withdraw from the study before they complete their treatment sequence it may cause rather serious problems such as biased results, decrease in the statistical power of study, even a conversion of the design to a disconnected design in which the basic treatment comparisons cannot be performed. In this study, the robustness of two treatments three periods dual balanced designs which enables the estimation of interested treatment comparisons using differences derived from within-subject measurements are evaluated by analyzing the performance measurements obtained by using A optimality criterion and the probability of generating a disconnected design.

Anahtar Kelimeler

• Crossover designs
• Subject dropout
• Robustness
• Disconnected designs
• Dual balanced designs

Kaynakça

1. Low J.L., Lewis S.M., Prescott P., 1999. Assessing robustness of crossover designs to subjects dropping out, Statistics and Computing, 9: 219-227.
2. Godolphin J. D., 2004 . Simple pilot procedures for the avoidance of disconnected experimental designs, Journal of Application Statististic, 53(1):133-147.
3. Majumdar D., Dean A. M., Lewis M. S., 2008. Uniformly Balanced Repeated Measurements Desıgns in the Presence of Subject Dropout, Statistica Sinica, 18: 235-253.
4. Bose M. Bagchi S., 2008. Crossover Design Allowing for premature Stopping, Utilias Mathematica, 75:273-285.
5. Zhao S.,2009(a). Repeated Measurement Designs under Subject Dropout, Quality and Production Research Conference, Chicago.
6. Zhao S., 2009(b). Crossover Design Under Subject Drop Out, ProQuest., Chicago.
7. Zhao S., 2010. 2−treatment crossover desıgn wıth small number of periods under subject dropout, http://interstat.statjournals.net/YEAR/2010/articles/1011001.pdf (Erişim Tarihi : 20.10.2014).
8. Matthews J.N., Henderson R., 2013. Two-Period, Two-Treatment Crossover Designs Subject to Non-Ignorable Missing Data, Biostatistics, 14(4):626-638.

9. Zheng, W., 2013. Universally Optimal Crossover Designs under Subject Dropout, The Annals of Statistics, 41(1): 63-90.
10. Chow S.C., Liu J.P., 2004. Design and analysis of clinical trials: Concepts and methodologies, Second Edition, John Wiley&Sons, New Jersey, p.181-183.
11. Zhou J., Yuan Y., Chen M., Coate B., Empirical power for higher-order crossover designs in comparative bioavailability clinical trials, poster, SUGI 30; 2005 Apr 10-13, Philadelphia(PA).
12. Jones B., Kenward M.G., 1989. Design and analysis of cross-over trials, Chapmen and Hall, New York, 152.
13. Laska E., Meisner M. Kushner H.B., 1983. Optimal crossover designs in the presence of carryover effects, Biometrics, 39: 1087-1091.
14. Ebbutt A.F., 1984. Three-period crossover designs for two treatments, Biometrics, Vol. 40, (1): 219-224.
15. Das A., 2002. An introduction to optimality criteria and some results on optimal block design, Design Workshop Lecture Notes, ISI, Kolkata, pp. 1-21.
16. Matthews J.N.S., 1990. Optimal dual balanced two treatment crossover designs , The Indian Journal of Statistics, Volume 52, Series B, Pt.3: 332-337.
17. Carriere, K C., Huang R., 2000. Crossover designs for two-treatment clinical trials, Journal of Statistical Planning and Inference, 87: 125-134.
18. Kershner R.P., 1986. Optimal 3-period 2-treatment crossover designs with and without baseline measurements, Proceedings of the Biopharmaceutical Section of the American Statistical Association, 21:152-156.
19. Low, J. L, 1995. The Design of Cross-Over Studies Subject to Dropout, PhD thesis, University of Southampton, ch4:19.