Causation and Correlations Assume that you have found an interesting - PowerPoint PPT Presentation

Causation and Correlations  Assume that you have found an interesting (new?) correlation between X & Y  What should you do?  1) schedule the Ss to return ( or start a new study that will have measures at two different times ) why ? to be able to do the cross-lagged analysis  2) during the delay between measures, think about possible third variables; add these to second test why? to be able to do the covariance analysis

Partials & Spurious Correls  theory-driven approach if the X-Y correlation is spurious via Z then prXY • Z will be zero if the X-Y correlation does not involve Z then prXY • Z will be the same as rXY  data-driven approach if prXY • Z = rXY then the X-Y correlation is not spurious via Z if prXY • Z is zero then the X-Y involves Z ( or a correlate of Z )

Sampling how do you choose a method? ask yourself how important it is to have a sample that accurately represents the target population if “not very”: convenience if “sort of”: simple random sampling if “very”: stratified random sampling then make sure that the method you selected won’t run into any statistical issues

Choosing a Correlational Method Surveys Observation What are you trying to measure? attitudes, values, beliefs, behavior and other unobservable attributes Is reactivity a serious problem? Is realism important? no yes Are you willing to invest time/effort? no yes

Aging Research  Hybrid Design 1 younger comparison #2 younger older comparison #1 if comparison #2 ( w/ cohort problem ) finds the same as comparison #1 ( w/ time-frame problem ), then OK i.e., if the two “younger” data same, all is well

Definitions ( and more )  Naturalistic Observation – studying behavior in everyday environments without getting involved key threat: reactivity (secondary: observer bias)  Participant Observation – studying behavior from within the target group key threats: reactivity + std. exptr bias (secdry: obsr bias) note: Partic.Obs. is not often possible, since no-consent observation can only occur when and where there is no reasonable expectation of privacy  Observer Bias – when the beliefs or expectancies of the observer ( consciously or otherwise ) influence what is recorded – note: inter-coder reliability must be . 90 +

Last-minute Questions  10 pm on Wed evening: http://www.justin.tv/directory/science_tech look for “ Uipsymeth ” stream if it asks for password: “exam3”