Sampling StudiesUrban PopulationPrevalenceCross-Sectional StudiesProbabilityProbability TheoryModels, StatisticalProbability LearningAlgorithmsBayes TheoremComputer SimulationMonte Carlo MethodTime FactorsChorionic Villi SamplingModels, GeneticMarkov ChainsEnvironmental MonitoringReproducibility of ResultsSpecimen HandlingLikelihood FunctionsSensitivity and SpecificityModels, BiologicalData Interpretation, StatisticalBlood Specimen CollectionModels, TheoreticalSample SizeStochastic Processes