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 ...

Medical research plays a vital role in advancing healthcare, improving treatment, and informing public health policies. However, it can be difficult to understand a study or whether it is trustworthy.

NPORS is an annual survey of U.S. adults conducted by Pew Research Center. Respondents may answer by paper, online or over the phone. They are selected using address-based sampling from the U.S.