Source material

Three data sets are associated with this case study. CS14Data1 contains data on measurements made at each site and each month in the river together with numbers of people sampled and numbers and percentages of samples found to be positive. Data collected from the river include the numbers of different species of snails recorded each month including the number of Biomphalaria species responsible for the transmission of bilharzia together with numbers infected. Data for the environmental variables (water flow velocity, pH, temperature and TDS) are also included in this file.

Three of the months (October, November and December) experienced heavy rains of above 900 mm and have been recorded as wet, whilst the other three months (January, February and March) experienced little or no rains and have been recorded as dry.

Human data are contained in CS14Data2. Each record contains the numbers of individuals sampled and the number of samples found to be positive during the study, categorised by site, distance from river, gender and age group: 5 − 9 years (regarded as children), 10 − 19 years (regarded as adolescents) and 20 years and above (regarded as adults). The average percentage of samples per month found to be positive has also been calculated. Everyone was eager to participate in the study as it gave them an opportunity to know their monthly worm status, and there were few occasions when individuals missed an examination.

Data are documented in CS14Doc1 and CS14Doc2, respectively.

The third data set CS14Data3 is a subset of CS14Data1 derived to analyse associations between snail numbers and environmental variable measurements.