TY - BOOK AU - Altman, D. G. PY - 1991 DA - 1991// TI - Practical Statistics for Medical Research. London: Chapman & Hall; ID - Altman1991 ER - TY - BOOK AU - Kirkwood, B. R. PY - 1988 DA - 1988// TI - Essentials of medical Statistics. London: Blackwell Science Ltd; ID - Kirkwood1988 ER -