This document discusses various statistical and epidemiological concepts: - Confidence intervals narrow as sample size increases and are calculated using standard deviation. - Independent t-tests compare two means, z-tests are for small samples, and paired t-tests compare two related samples. - Notification of diseases is a legal duty for doctors and relates to secondary prevention. - Special surveillance is done for dengue fever, pneumococcal pneumonia, and hepatitis A. - Population pyramids describe the age-sex relationship of a population affected by birth rates.