This document discusses key concepts in statistics including population, sample, qualitative and quantitative data, histograms, opinion surveys, and circle graphs. A population is the overall group being studied, while a sample is a subset of the population that is actually surveyed. Qualitative data falls into categories while quantitative data is numerical. Histograms display quantitative data intervals as bars and circle graphs illustrate parts of a whole using percentages. Opinion surveys collect data based on opinions.