The Mann-Whitney U Test, also known as the Wilcoxon Rank Sum Test, is a non-parametric statistical test used to compare two samples or groups. The Mann-Whitney U Test assesses whether two sampled ...

Researchers studying hidden populations—including injection drug users, men who have sex with men, and the homeless—find that standard probability sampling methods are either inapplicable or ...

Pew Research Center designed this study to assess the current state of online survey sampling methods – both probability-based and opt-in – and determine their accuracy on general population estimates ...

Celeste K Wong, Pamela L Horn-Ross, Gilbert C Gee, Salma Shariff-Marco, Thu Quach, Laura Allen, Roxanna Bautista, Patricia Quema La Chica, Winston Tseng, Pancho Chang, Christina A Clarke, Juan Yang, ...

Historically, public opinion surveys have relied on the ability to adjust their datasets using a core set of demographics – sex, age, race and ethnicity, educational attainment, and geographic region ...