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UASTAT141Ch11-13 - Ch 11 13 Gathering Data Defn An...

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Ch. 11 – 13 - Gathering Data Def’n: An observational study is a study where a researcher observes characteristics of subjects in samples from populations of interest. An experiment is a study where a researcher applies different treatments to different subjects and observes the outcomes. Drawing conclusions : 1. Infer to a larger population (Population) 2. Factor causes change in response (Causal) Both types of study allow for #1, but only a properly designed (and randomized ) experiment allows for #2 to be valid. Experiments are not always feasible. Sampling Def’n: A sampling frame is the list of subjects in the population from which the sample is taken. A random sample is a sample drawn in such a way that each element of the population has a chance of being selected. If chances are all the same Æ SRS of size n - e.g. A deck of cards: picking a card is a simple random sample. Moreover, placing the card back in the deck is a sample with replacement . Otherwise, there is sampling without replacement .
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