shoebill1

shoebill1

shoebill1

Match the definition with correct term

The target group about which you'd like to make inferences

  1. Sample
  2. Population
  3. Summary statistic
  4. Anecdote

Match the definition with correct term

The individual unit on which you make observations

  1. Parameter
  2. Sample
  3. Case
  4. Census

Principles of Data Collection for Inference

case/observational unit - the individual unit on which you make observations (a row in a data frame) [In arbuthnot data set, a case is a single year]

population - the target group of observational units about which you'd like to make inferences [size of the population: \(N\)]

sample - a subset of the population on which you have data [size of the sample: \(n\)]

anecdote - very small sample of data collected haphazardly [usually \(n = 1\)]

census - sample = population [complex, expensive, and sometimes impossible to achieve]

Sampling considerations

You're a senior Psychology major conducting a study that examines procrastination among Reed students. How should you select a sample?

  1. Post a link to your survey on your Facebook page

    • \(n \approx 100\)

  2. Get a list of Reed student emails from the Registrar, take a simple random sample (SRS), and email that sample

    • Initial \(n = 100\), Final \(n = 34\)

landon-fdr

Landon v. FDR, 1936

Literary Digest polled 10 million Americans, 2.4 million responded.

N = 128 million, n = 2.4 million

Prediction: 43% for FDR

Result: 62% for FDR

What went wrong?

Literary Digest surveyed

  • magazine subscribers
  • registered car owners
  • registered telephone owners

These groups have a much higher income on average than the typical american. In 1936 the Great Depression is still in full swing, so the typical (poorer) american was more supportive of FDR.

Their sampling method was biased (not representative).