A quality control manager wants to see how many defective products come off the line on average per day. They select every tenth unit produced on the line and inspect it to see if it is defective. What type of sampling method is this?

A store is interested in whether they should adjust their store hours, so they choose a random day to poll all people entering the shop and ask them if they would prefer the store to change their hours. Is this a simple random sample? Can we assume this is a representative sample?

A superintendent of a school system is interested in how the teachers working at the schools feel about the current professional development offerings, so they use the employee dashboard to randomly select 60 teachers for their survey. As it happens, approximately two teachers from each grade are chosen, and there is about the same number of teachers for each major discipline. Is this a simple random sample? Is it a representative sample?

A regional manager runs the day-to-day operations of three branches of a chain restaurant. Each location is roughly the same size and employs approximately the same number of workers. The manager is interested in streamlining policies across each location, so he decides to survey 10 random employees in each branch about certain processes. Is this a simple random sample? Is it a representative sample?

A quality control manager wants to see how many defective products come off the line on average per day. They select three random cases of units at the end of the day to test how many defective units are in one of the three cases. What type of sampling method is this? 

A quality control manager wants to see how many defective products come off the line on average per day. They use a random number generator to select 100 of the 1500 units produced that day and tested whether they were defective. What type of sampling method is this?

A quality control manager wants to see how many defective products come off the line on average per day. They take 10 random units produced over the course of the day from each of 10 machines to test if they are defective. What type of sampling method is this?

What is replication in an experiment? Why is replication important?

"Researchers in Japan tested the effect of cannabidiol (CBD) in treating late teenagers with social anxiety disorder (SAD). Thirty-seven 18- to 19-year-old teenagers with SAD took part in the study. The patients were assigned at random to receive a daily dose of either CBD or a placebo for 4 weeks. Symptoms were measured using The Fear of Negative Evaluation Questionnaire and the Liebowitz Social Anxiety Scale at the beginning and end of the treatment. (Source: Frontiers in Psychology)

Identify a potential problem with the experimental design being used and suggest a way to improve it."