Which is an example of simple random sampling?
1.Distributing 20 surveys to a group of friends
2.Selecting and contacting every seventh student from the list of current students
3.Handing out surveys to all currently enrolled students and asking that they return the completed surveys to the library
4.Using a random number generator to select 20 student identification numbers and having those 20 students complete a survey
Question 2
A researcher wishes to study the relationship between the level of background noise and mental concentration. The treatment (noise level) will have three levels: no noise, low-intensity noise, and high-intensity noise. the subjects are to be divided into three groups, and each group is to receive one of the treatments. He has available to him a set of 60 female volunteers and a set of 90 male volunteers. What experimental design strategy would help him eliminate the introduction of gender as a confounding variable?
1.stratified sampling
2.replication
3.blocking
4.systematic sampling
5.double-blind trials
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