Adding a participant variable to a design with an existing independent variable is one way to increase external validity. True or False

An education expert is researching teaching methods and wishes to interview teachers from a particular school district. she randomly selects ten schools from the district and interviews all of the teachers at the selected schools. which type of sample did she use in this study? a)systematic sample b)probability sample c)stratified sample d)cluster sample

The lifeguard at the local beach record the tides each day the chart below shows the high and low tides over two days

What’s the reason for not digging up aztec ruins in modern mexico city