A population is the whole group the crew cares about, and a sample is the part it actually asks. A parameter is a number about the population; a statistic is a number from the sample that estimates it. Random selection makes a sample fair, and different random samples give different statistics that scatter around the parameter. Sample surveys, experiments and observational studies each use randomization differently, and a report is only as good as who was asked, how they were chosen and what they were asked.