Describe the 4 different types of samples and whether they're random or not.
Simple Random = selection of one unit does not affect the selection of another, each unit has an identifier number, each unit has an equal chance of being selected
Sequential/systemic random sample= selection of one unit does influence the selection of another, i.e. the first one is chosen randomly and then after that every 17th unit is chosen.
Randomized block study: subjects/units organized into blocks, once a block is randomly chosen, all those units/subjects are in the study, this is NOT a truly random sample
Convenience sample: non-random sample, no element of random sampling, external validity seriously questioned (SCCO student research is usually convenience sample)