Sampling Sampling Probability Sampling Scientific Non Probability Sampling Non Probability Sampling Accidental Haphazard or Convenience Sampling Purposive Sampling Modal Instance Sampling Expert Sampling Quota Sampling Heterogeneity Sampling Snowball Sampling An Example We want to know what proportion p of the adults in the U S voted in the last election p is a parameter of the population Unless we ask every adult we won t know the value of p We can however take a small sample and use the result to estimate the proportion We take a scientific sample of 1700 adults and ask them if the voted in the last election 795 say the have voted p 795 1700 0 468 or roughly 47 We could then say that 47 of the adult population voted in the last election We need say how confident we are in this estimate and what the margin of error is Quick Estimate for Margin of Error for 95 Confidence Level 1 where n is the sample size n In our example the margin would be 1 0 024 1700 or roughly 2 4 Confidence Statement In this example we would say something like We are 95 confident that 47 of the adults voted in the last election with a margin of error of 2 4 What does this confidence statement mean It means that if we were to repeat the sample many times that 95 of the time the results would be within 2 4 of the actual population proportion
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