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The mean speed of sound between a given position & a listening station may vary in a range between 1470 and 1510 m / s , due to geographical variations in the sound speed profiles & ray geometry . Raitz and Brunn tied the development of farm journals to geographical variations and the growing dominance agriculturally of those regions . Path analysis allows predictions of population behaviour in relation to geographical variations . More deaths could be attributed to geographical variations in mortality rates . The course addresses state of the art methodologies for investigating the environmental contribution to geographical variations in cancer incidence and cancer risks related to low level widespread carcinogen exposures , including the role of biomarkers and molecular epidemiology .