PSC 41 Lecture Notes - Lecture 9: The Literary Digest, Internal Validity, Sampling Error
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How would you graph the data: the predictor variable is studying period. This variable is categorical since we are comparing with just two periods. You need to know if your findings relate to the entire population. Research conducted with a representative sample will have stronger external validity: external validity is most important when establishing a frequency claim. Causal claims are all about internal validity: types of samples, probability, uses random sampling, every member has an equal likelihood of being selected, representative, sample will be very similar to the population. No sample bias: strong external validity, nonprobability, does not use random sampling, different members have different likelihoods of being selected, not representative, sample may not be similar to population, sample bias. Weak external validity: error in sampling, error is the extent to which the sample differs from the population, sampling error (random error, no two samples will be the same.
