Question: Do teachers have tattoos?

Population: All teachers at North Penn High School
Parameter of Interest: the true proportion(%) of teachers at North Penn that have tattoos

I would stand at the front of the building at 2:49pm and ask teachers on their way out if they'd like to volunteer for a survey about having a tattoo.

I would place surveys in their mailboxes and ask them to return them to me by the end of the week.

<Repeat for all types of bias discussed>