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PSYC 217
Catherine Rawn

NOVEMBER 14 INFERENTIAL STATS LEARNING OBJECTIVESExplain the relationship betw sample and popDescribe how the Smarties activity illustrates why we use stats to analyze our sample dataDescribe at least 3 errors in judgement ppl commonly makeDiscuss the importance of relying on base rate data from large samples rather than small samplessingle casesDefine gamblers fallacy In psych science the goal is truthIn any study we need to figure out if our results was due to chance or if it really represents the truth o Therefore we analyze our data using stats o Inferential stats taking sample and making inferences about it o how likely is that our result is due to randomness or a real effectAvoid relying on humans biased thinkingNeed to think about probability Probability choose a random sample of smarties Blue Brown Green Orange Red Yellow Purple Pink Predicted 125 125 125 125 125 125 125 125Observed 0 0 273 1820 182 9 273 frequencyN Observed 0 0 0 619 0 319 319 419 frequency 2N Observed 0 960 960 1260 860 1360 360 760 frequency 7NData from full class was better estimate of the population because bigger sample size better representation o Small sample sizemore likely to get weird individuals and skew data Population vs samplePop level o In the smarties factory how many of each colour are madeProbabilistic trend o The proportion of each colour of Smarties in the pop of smarties at the factorypop o Try to estimate using samplesRandom sample o In any funsized packet of Smarties how many of ea colour are thereas our sample size increases the pattern in the sample will better represent the truth in the pop Samples are imperfect assessments of overall probabilitiesProbabilistic trend o What is the true overall effect o Doesnt need to be true in every case for it to be true generally o Eg Regression line as the best fit to summarize all the data pts doesnt perfectly explain every data ptRandom sample o We can take a random sample from the pop to estimate the true effect o As our sample size decreases our estimate is more likely to be wrongEg A certain town is servedby 2hospitals o In the larger hospital 45 babies born ea day and in smaller hospital 15 babies born ea day o About 50 babies are boysbut varies by day sometimes higherlower o For 1 yr ea hospital recorded the days on which more than 60 babies were boys which hospital do you think recorded more such days smaller hospital more likely to be deviant Inferential stats
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