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, ...

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 ...

Biological samples can be highly susceptible to changes over time, which often occur when they are removed from deep refrigeration. Degraded samples can produce spurious results in research. To ...