An amazon seller asks all of their customers to participate in a survey for to get a free product. A sample created from this method may suffer from which of these biases? self-selection bias area bias no bias present social desirability

If you have a study design that requires two different samples, what sort of test might you consider?    Matched samples test    Independent samples test

Cite a statistical experiment and its sample space.

From 2003 to 2007, a group of doctors studied the effects of a new attention deficit disorder medication on adults. To compare results, the doctors gave half their patients the new medication and maintained the other half of their patients on their current medication. What is being used in this example? The effect of a treatment unit The placebo effect A control group Sampling error O Voluntary response bias