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Stanford University...volunteered to do surveys for money or prizes and were not randomly sampled from the American adult population (we refer to the latter as "opt-in" samples). Our

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Page 1: Stanford University...volunteered to do surveys for money or prizes and were not randomly sampled from the American adult population (we refer to the latter as "opt-in" samples). Our
Page 2: Stanford University...volunteered to do surveys for money or prizes and were not randomly sampled from the American adult population (we refer to the latter as "opt-in" samples). Our
Page 3: Stanford University...volunteered to do surveys for money or prizes and were not randomly sampled from the American adult population (we refer to the latter as "opt-in" samples). Our
Page 4: Stanford University...volunteered to do surveys for money or prizes and were not randomly sampled from the American adult population (we refer to the latter as "opt-in" samples). Our