@article{oai:meisei.repo.nii.ac.jp:00000319,
 author = {塚田, 真一 and Tsukada, Shinichi},
 issue = {1},
 journal = {教育学部研究紀要},
 month = {Mar},
 pages = {63--83},
 title = {Unbiased estimators for the covariance matrix under a monotone incomplete sample},
 year = {2011}
}