{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

# Lecture13 - lecture 13 Samples and Surveys Sampling...

This preview shows pages 1–5. Sign up to view the full content.

lecture 13, Samples and Surveys, Sampling Distributions I 1 / 21 Samples and Surveys Sampling Distribution Sampling Distribution of the Sample Mean Central Limit Theorem (CLT) lecture 13, Samples and Surveys, Sampling Distributions I Outline 1 Samples and Surveys 2 Sampling Distribution Sampling Distribution of the Sample Mean 3 Central Limit Theorem (CLT)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
lecture 13, Samples and Surveys, Sampling Distributions I 2 / 21 Samples and Surveys Sampling Distribution Sampling Distribution of the Sample Mean Central Limit Theorem (CLT) lecture 13, Samples and Surveys, Sampling Distributions I Samples and Surveys Samples Want to learn some numerical facts about a population (called population parameters , e.g., μ , σ ) Census (A comprehensive survey of the entire population) Cost and time constraints generally prohibit carrying out a census; in some cases a census is not feasible. Examine part of the population, called the sample , and make inferences from the sample about the population Parameters are estimated by sample statistics , i.e., numbers which can be computed from a sample (e.g., ¯ x , s ) Estimate = Parameter + Bias + Chance Error Bias: systematic error in an estimate. Bias should be avoided as much as possible in survey, by choosing samples that reflect the mix in the entire population (be representative ) How sample is chosen matters a lot.
lecture 13, Samples and Surveys, Sampling Distributions I 3 / 21 Samples and Surveys Sampling Distribution Sampling Distribution of the Sample Mean Central Limit Theorem (CLT) lecture 13, Samples and Surveys, Sampling Distributions I Samples and Surveys The Literary Digest Case, revisited 1936 election: Roosevelt vs Landon; Roosevelt’s percentage: The Digest prediction: 43%; The election result: 62%; Literary Digest interviewed 2.4 million potential voters (the largest number of people ever replying to a poll!) (total voted: about 45 million) Literary Digest went bankrupt soon after the 1936 presidential election... In contrast, Gallup interviewed only 50,000 people, and correctly forecast the Roosevelt victory ( Gallup predicted 56%).

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
lecture 13, Samples and Surveys, Sampling Distributions I 4 / 21 Samples and Surveys Sampling Distribution Sampling Distribution of the Sample Mean Central Limit Theorem (CLT) lecture 13, Samples and Surveys, Sampling Distributions I Samples and Surveys Example, The Literary Digest, revisited, ctd Q: What went wrong with Literary Digest ’s method? Literary Digest ’s sampling procedure: mailed questionnaires to 10 million people on telephone books and club membership lists, about 24% responded; I Mistake #1: in 1936, poor people were more likely not to have telephones or join clubs; Systematic tendency in the sampling procedure to exclude one kind of person or another from the sample selection bias ; I Mistake #2: about 76% surveyed people did not respond, and only the respondents were taken into account.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 21

Lecture13 - lecture 13 Samples and Surveys Sampling...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online