Course Notes - Department of Mathematics and Statistics

8 Contingency TablesFred’s GardenFred decided to start a flower garden. To do so he collected somecuttings from his friends. He collected them all throughout the year,although some of his friends suggested that cuttings planted in thewinter would not do so well. Since Fred was not a very good gardenerhe expected a lot of flowers to die anyway. Fred recorded the survival ofcuttings collected in both winter and summer, this can be summarizedin the table below.OutcomeTime of cutting Cutting Alive Cutting Died TotalWinter 263 217 480Summer 115 365 480378 582 960Is there any evidence that there are more flowers than would beexpected during the winter months?Fred’s wife, Carol, decided that she wanted to go on a holiday to somewhereforeign and exotic compared to the traditional routes. She suggestedsomewhere in Western Africa. Fred thought this sounded likefun, however he was paranoid about river-blindness (microfilariae infection),and wanted to decrease the risk of contracting it. He found astudy that thought there seemed to be a difference in risk dependingon whether you were in the savannah or the rainforest areas of SierraLeone (McMahon et al. 1988, Trans Roy Soc Trop Med Hyg 82; 595-600). The information is summarized below in a contingency table.Microfilariae InfectionArea Yes No TotalRainforest 541 213 754Savannah 281 267 548822 480 1302139