mid term review - Midterm 1 Review Part I: Gathering Data...

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1 Part I: Gathering Data Population: the entire group of individuals that we want information about. Any numeric value from the population is a parameter. Sample: subset of the population that we actually examine to gather information about the population. Any numeric value from the sample is a statistic. Sampling Designs Make sure you have the big 4 memorized: SRS, Systematic, Cluster and Stratified. Remember, most students struggle with telling stratified from cluster samples. Focus on any of the three differences that resonates with you to tell them apart: Stratified Cluster We divide into groups Groups are already divided by something/someone other than us Subjects within group are similar for some characteristic or set of characteristics Subjects within group are dissimilar We choose a sample from group We choose entire group V oluntary Response Sampling: Sample chooses themselves. (Web survey, call-in polls) Convenience Sampling: We choose people that are easiest to reach. Simple Random Sampling (SRS): We choose people at random (i.e. picking names out of a hat). Each member of the population has an equal chance of being included. Systematic Sampling: We choose every nth item. Cluster Sampling: The population is already divided into groups that are dissimilar on characteristics. We then randomly select entire clusters and combine 1 or more clusters to get our overall sample. Stratified sampling: We first divide our population into groups ( we did the dividing!) that are similar on some characteristic or set of characteristics, then take an SRS from each group ( sample from groups, not entire group! ) and combine those samples into our overall sample. Multistage Random Sampling: combining a variety of sampling methods ***If each member does not have an equal chance of being selected, then we say that the sample is biased !! Types of Bias Any question about biases will ask for the most prevalent type of bias, so even if you can argue that a few types are answers (they usually will be), be on the lookout for those keys to let you know what the problem being tested is! Undercoverage: Entire population targeted is not included in the design of the sample. o Be on the lookout for any mention of a certain group in the sample design, if they mention they only sampled females, or people of a certain age group, or people
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2 from a certain region – check that the group mentioned is the same as the population they are interested in. If not, you have undercoverage! Non-response: an individual selected cannot be contacted or refuses to cooperate. o Any mention of choosing people into the sample and people not responding – whether not being home for interview or phone call, refusing to participate, etc… Response Bias: Interviewee’s responses are influenced by the interviewer.
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mid term review - Midterm 1 Review Part I: Gathering Data...

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