4.1 CLUSTERS AND CLUSTER SAMPLES By Keaton Kemnitz & Esteban Luis Asencio Otero Garcia de Guantanemo Masson

CLUSTERS  When a population is divided into smaller groups, or clusters, that mirror the characteristics of the population

CLUSTER SAMPLE  To make a cluster sample, divide the population into clusters.  Then choose an SRS, or stratified random sample, of the clusters.  All individuals in the chosen clusters are included in the sample.

4.1: WHAT NOT TO DO IN A SURVEY

BIAS  Failure to use random sampling often results in bias  Bias are systematic errors in the way a sample represents the population  The design of a statistical study shows bias if it systematically favors certain outcomes

VOLUNTARY RESPONSE SAMPLE  A voluntary response sample consists of people who choose themselves by responding to a general appeal. Voluntary response samples show bias because people with strong opinions (often in the same direction) are most likely to respond

CONVENIENCE SAMPLE  Choosing individuals who are easiest to reach results in a convenience sample  Convenience samples are prone to large bias due to this fact