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Sampling

1.
Almost always when doing an observational study, such as a survey, students have trouble getting the sampling right. This can also occur, but is less common, in selecting experimental units for an experiment. Unless you have a frame (list of sampling units in the target population), and deliberately sample the units from the frame by a probability sampling scheme, you are almost certainly obtaining a suspect sample. If this is the case, in your final project report you had better justify your sampling method (this can be often be done in terms of lack of time or other resources), tell what is wrong with it, and tell what you should have done to get it right. If you are not clear about this point, see me.
2.
Validate your sample whenever possible. This means collecting data on the sampled units that can be compared to known population quantities to help establish the representativeness (or lack thereof) of the sample. For example, if your sample of WPI students is 60% female, you would rightly suspect that the sample is not representative of all WPI students. In your final project report, detail validation of your sample, or tell why it was not possible to do it.


next up previous
Next: Data Disk Up: Other Important Stuff Previous: What Do I Put
Joseph D Petruccelli
5/26/1998