A growing share of polling is conducted with online opt-in samples. 1 This trend has raised some concern within the industry because, while low participation rates pose a challenge for all surveys, ...

Analytical methods for detecting opium alkaloids such as morphine, codeine, thebaine, papaverine and noscapine play a critical role in food safety, public health and forensic toxicology. These ...

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 ...

Accurate quantification of cyanide in biological matrices is essential for clinical diagnosis, forensic investigation and occupational exposure monitoring. The principal challenge lies in the low ...

Power analyses and sample size calculations are important parts of many research projects. Often, before data are even collected, it is necessary to calculate and justify the required sample size for ...