COMM291_CLASS3 - COMM 291 202 10 January 2017 CLASS 3...

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COMM 291, 202 10 January 2017 CLASS 3 Chapter 2 - Data quality o Data origins? o Incompletely or poorly defined variables -> need operational definitions o Spurious activity => assume data is accurate o How was data collected? - Time series data -> collected longitudinally - Cross-sectional data -> collected at 1 point of time Chapter 3 - Data origins o Voluntary surveys -> usually worthless o Experimental studies -> higher, quality data § Actively manipulate variables o Observational studies o Secondary surveys - 3 ideas of sampling o Estimate part (sample) of the whole (population) § Representativeness -> hard to choose § Biased sample: characteristics of sample differ from corresponding characteristics of the population o Randomize -> use “chance” process § Not subject to biases § Any 2 samples different from one another § Sampling variability (error): differences between 2 samples *error ≠ mistake, error = variance between truth and data* o Sample size matters -> population size just needs to very large - Methods of sampling o
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