Ronaldo Iachan, PhD
ICF International, Calverton, Maryland
Dr. Iachan, a senior statistician, has 30 years of experience in statistical methods and applications, particularly in the areas of survey sampling design and analysis. For ICF, Dr. Iachan provides statistical expertise across divisions in projects in the areas of health, education, and social studies. He was a professor at Iowa State University and at the University of Wisconsin–Madison. He has served on ICF’s IRB for 12 years, and has been a statistical editor for the Journal of the American Medical Association for the past 15 years. He has extensive experience in statistical design and analysis, with more than 30 refereed articles published in statistical methods,. Dr. Iachan has extensive experience providing sampling and survey design support for many cancer-related projects for the Centers for Disease Control and Prevention (CDC) and other agencies, including cancer registry studies and heart disease prevention.
364 – Nonprobability/Web Sampling and Data Analysis
Comparing Non-Probability and Probability Sample Estimates
Ronaldo Iachan, PhD
ICF International, Calverton, Maryland
John Boyle
ICF
Eric Miller
ICF
The increasing use of internet panel surveys has led to a growing need for inferences from these samples that are generally selected with non-probability sampling methods from a very large panel population. Also lacking is evidence of the validity of these samples at least in the sense of representation, coverage, and comparability with probability samples of similar populations. This paper first describes the weighting methods used to generate valid estimates. It then explores the development of variances and confidence intervals for these weighted samples, and uses these to compare the survey estimates with probability sample estimates. This research uses data from a series of internet panel studies; specifically, we used the data from the study conducted in Los Angeles County. We compare the results with local data from the Behavioral Risk Factor Surveillance System (BRFSS) and from the California Health Interview Survey (HIS).