Week 3 Notes
Week 3 Notes STAT 200
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This 2 page Class Notes was uploaded by Kelsey Marr on Thursday February 5, 2015. The Class Notes belongs to STAT 200 at Pennsylvania State University taught by Andrew Wiesner in Winter2015. Since its upload, it has received 63 views. For similar materials see Elementary Statistics in Statistics at Pennsylvania State University.
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Date Created: 02/05/15
Stat 200 Wiesner Week 3 Notes Gathering Data 0 Three Research Strategies 0 Sample survey 0 Observational study 0 Experiment 0 Two ways to get data 0 Nonprobability methods Convenience or haphazard sample 0 Ex use our class Volunteer Ex visit website and vote in some poll 0 Probability methods Simple random sample SRS Where each subject has equal chance of being selected Strati ed random sample 0 The population or subjects are grouped by some distinction race class standing etc then a SRS is taken from each stratagroup Cluster sample 0 Random selection process is not one at a time but a group at a time 0 Ex randomly select a ight and interview all passengers or randomly select a section of a class and interview all students in that section The purpose of using probability methods is the use of randomness the random selection Using such techniques we gather a sample that represents some population of interest all PSU students etc Doing this then allows us to infer our sample results back to population 0 Ex if we randomly selected 1000 PSU students and 62 said campus was safe at night we can infer that 62 of all PSU students think campus is safe at night 0 In random surveys we have a margin of error 0 Ex an error range from which the true proportion falls within 0 This margin of error can be approximated by 1square root of n where n is the sample size A common industry margin of error standard is 3 which equates to a sample size of about 1100 o Bias that can appear in studiessurveys 0 Response bias subjects don t respond honestly o Nonresponse bias large percentage of sample doesn t respond 0 Selection bias we select subjects that don t represent the population of interest Observational Study 0 Where we observe subjects in their quotnatural statequot 0 Experiments 0 Where we randomly assign some treatment 0 Biggest difference between these two is that for an experiment we can conclude causecasual effect but for observational study only a relationship 0 In an experiment or observational study we have an explanatory variable and a responseoutcome variable Ex smoking vs lung cancer 0 Explanatory variable smoking 0 Response variable lung cancer Ex height and weight 0 Explanatory height 0 Response weight Blinding of subjects is done so subjects don t know what treatment they are receiving 0 Done to avoid placebo effect 0 Blind experiment researcher does not know what treatment subjects receive This is done to avoid experimenter effect 0 If both subject and experimenter are blinded we have a double blind study
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