review for exam two - The variability of a statistic is...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Review for exam 2 (mat 221) Principles of experiment design: compare, randomize and repeat Simple random sample (SRS) : An SRS gives every possible sample of a given size the same chance to be chosen. To choose a stratified random sample , divide the population into strata , groups of individuals that are similar in some way that is important to the response. Voluntary response samples, in which the respondents choose themselves, are particularly prone to large bias. Undercoverage occurs when some groups in the population are left out of the process of choosing the sample. Nonresponse occurs when an individual chosen for the sample can’t be contacted or does not cooperate. Bias concerns the center of the sampling distribution . A statistic used to estimate a parameter is unbiased if the mean of its sampling distribution is equal to the true value of the parameter being estimated.
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: The variability of a statistic is described by the spread of its sampling distribution . The spread of is determined by the sampling design and the sample size n. statistics from larger probability samples have smaller spreads . To reduce bias, use random sampling. To reduce variability, use larger sample. Variability of statistics is usually reported by giving a margin of error for conclusions based on sample results. Approval of an institutional review board is required for studies that involve human or animals as subjects. Human subjects must give informed consent if they are to participate in experiments. Data on human subjects must be kept confidential. Multi Rule: if A and B are independent P(AB) = P(A) * P(B) disjoint e independent o S j P(A) = P(AB) +P(AC) B e C o S j...
View Full Document

This note was uploaded on 06/16/2011 for the course MATH 221 taught by Professor Na during the Spring '10 term at University of North Carolina School of the Arts.

Ask a homework question - tutors are online