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Details Title: Elem survey sampling Description: GWU - Stat 187 Total Flash Cards: 35 Created: 01/28/2005 16:27:04	To study from this set of flash cards, or to create your own your own study flash cards, register HERE. If you are already a registered user, CLICK HERE.
Cards Term variance Definition measure of variability or measuring the deviation from the mean Term Central Limit Theorem Definition As the number in the same increases the Sum of all x's across n tends toward normal distribution Term Tchebysheff's theorem Definition for any k ge 1, at (1-1/k squared) of the measurements in any set must lie with in k SD of their mean Term sampling distribution Definition closely approximates a normal distribution if n is reasonably large but no more the 20 percent of the total population Term 2 measures of variable dependence Definition 1. covariance 2. simple coefficient of linear correlation Term coefficient of correlation Definition between -1 and 1 Term purpose of sample surveys Definition to estimate numerical characteristics called parameters like mean, total, or variance Term Element Definition object on which a measurement is take Ex. a registered voter in community Term Population Definition a collection of elements about which we wish to make an inference Ex. collection of voters in a community Term sampling units Definition nonoverlapping collection of elements from the population that covers the entire population Ex. households Term frame Definition list of sampling units Ex. list of all registered voter's households Term sample Definition a collection of sampling units drawn from a frame or frames Term probability samples Definition sample designs based on planned randomness Term simple random sampling Definition selecting a group of n sampling units in a way that each sample of size n has the same chance of being selected Term stratifeid random sample Definition dividing the population elements into 2 or more groups (strata) and select a simple random sample from each group Term cluster sampling Definition divide the population into groups by simple random sample then sample items within the cluster Term systematic sample Definition selecting every nth person Term quota samples Definition selecting randomly until reach a limit that matches the population (in all determining factors) Term Gallup telephone samples Definition unclustered directory-assisted, random-digit telephone samples - proportuate stratified sampling design Term "listing" bias Definition differences in population between unlisted and listed telephone customers systematicly effects survey results of only listed telephone numbers Term Errors of observation Definition -when recorded data deviates from the truth -by sampling coverage or nonresponse due to interviewer, respondent, instrument, or method of data collection Term sampling error Definition the deviation between an estimate from an ideal sample and the population environment Term errors of coverage Definition the sampling frame does not matchup perfectly with the target population Term nonresponse Definition 3 ways: 1. inability to contact element 2. inability for respondent to answer 3. refusal to answer Term What are the benefits and problems of personal interviews? Definition benefits: usually answer questions and able to note reaction and eliminate misunderstandings problems: cost and trained interviewers Term What are the benefits of telephone interviews? Definition interviews can be supervised less cost random digit dialing (only 20% of numbers are residential) Term Benefits and problems of Self-Administered Questionaires Definition lowest rate of response low costs Term Direct observations Definition usually not studies with people or using medical records Term What are some methods to reduce errors in surveys? Definition 1. Callbacks - use different times 2. rewards to participate - offered only after being randomly selected 3. train interviewers 4. check data 5. carefully planned questionaires Term Sample survey design Definition the procedure for selecting the sample Term simple random sampling Definition a type of sampling procedure in which a sample of size n is drawn from a population of size N such that every possible sample of size n has the same chance of being selected Term stratified random sample Definition seperating the population elements into nonoverlapping groups and then selecting a simple random sample Term What are three reasons to stratify? Definition 1. produce a smaller bound on the error of estimation 2. cost 3. to find information about each strata (domain) Term What three factors are used to allocate samples when stratifying? Definition 1. total number of elements in each stratum 2. the variability of observations within each stratum 3. the cost of obtaining an observations from each stratum Term What are the three methods of stratifying? Definition 1. proprotional 2. Neyman 3. Optimal