Exam 3 Notes

Exam 3 Notes - Lesson 9: Sampling and Confidence Intervals...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Lesson 9: Sampling and Confidence Intervals for Proportions Some commonly used probability sampling methods: 1. Simple random sampling : Every combination of n individuals within the population has an equal chance to be the sample. A simple random sample is usually picked by "lottery" methods. 2. Stratified sampling : The population is divided into important subgroups (e.g. East and West) which are groups of individuals or subjects that are similar in a way that may affect their response. 3. Cluster sampling : The population is divided into several subgroups by geographic proximity or closeness of individuals to each other on a list. In stratified sampling we create the subgroups based on some criteria – ethnicity, geographic region, and then random sampling of individuals or subjects is done. In Cluster sampling, clusters of individuals or subjects are randomly sampled. Some methods often used that are NOT probability sampling methods: 1. Self-selected sample : volunteer sample with no random selection process imposed by the researcher. Examples are polls done at web sites and television polls in which viewers are asked to phone in their opinion. 2. Haphazard sampling : The pollster wanders around an area (like the Hub or a downtown street) and haphazardly asking people to participate. 3. Convenience sampling: The sample is an available group (say, our Stat 200 class) and no probability methods are used for selection. Other Survey Biases Response bias : (false answers biased toward the most "acceptable" answer) Non-response bias : (systematic refusal of some people to answer certain types of questions) Wording of questions : (making one answer seem the most reasonable to give) Selection bias : results when the sample selected does not represent the population of interest. Chapter 10: Confidence Intervals for Proportions Confidence Interval and Confidence Level A confidence interval : is an interval, computed using sample information, that estimates the value of a population parameter. A confidence level : is the probability (often expressed as a percent) that the procedure used to determine a confidence interval gives an interval that actually includes the (unknown) value of the population parameter. In other words, a confidence level is the fraction of times the procedure works by "capturing" the population value. Calculating a general confidence interval: Sample statistic ± multiplier × Standard Error. Sample statistic is a summary value for an observed statistic. The standard error is the estimated standard deviation of the sampling distribution of the statistic. The multiplier controls the confidence level and is determined using either a standard normal curve or a t-distribution. We’ll cover the t-distribution at a later time. The multiplier times the standard error is referred to as the margin of error
Background image of page 1

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

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

Exam 3 Notes - Lesson 9: Sampling and Confidence Intervals...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online