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CKelly - Statistics
Statistics - Chapter 22
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04/18/2005

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Term
Unemployment Rate?
Definition
The percentage of the civilian labor force that is unemployed.
Term
What is the Bureau of Labor Statistics?
Definition
The agency in charge of the employment studies and statistics,
Term
For the Current Population Survey monthly report, how many are interviewed by the field staff of the Bureau of Labor Statistics?
Definition
1,700 staff members interview close to 110,000 people ( roughly 1/10th of a million )
Term
In the 1990 redesign of the Current Population Survey how many Primary Sampling Units (PSU) were there?
Definition
There were 2,007 Primary Sampling Units, each being a city or a county.
Term
Why are the interviews restricted to the same 792 PSU’s out of the 2,007 first made?
Definition
So that the PSU’s in each of the 792 strata will resemble each other in characteristics:
-like number of male and female heads of household
-number of workers in retail trade, etc.
Term
What are USU’s?
Definition
Each of 792 PSUs was divided into Ultimate Sampling Units. A USU consists of 4 housing units each.
Term
At the second stage, what are selected at random?
Definition
Some USU’s are selected at random and every person age 16 and over are added to the sample for the Current Population Survey
Term
Following stage one and two, how many samples are made in the early 1990s and why that many different samples are made?
Definition
16 different samples are made so that rotation of part of the sample can be possible. After put into the sample, a housing unit is kept for 4 months, dropped out dropped out for the next 8 months, and again brought back for final 4 months.
Term
What is the threshold size of a sub-sample allowed in estimation of numbers in Employment and Earnings?
Definition
A thousand estimates for numbers in Employment and Earnings are done and when a sub sample size is below 50, no estimate is undertaken.
Term
Why not change the housing unit every month in stead of keeping it for 4 months and bringing back for final 4 months with a break for 8 months?
Definition
That way a lot of money is saved. Also the overlap therein helps estimating the monthly change in Employment and Unemployment.
Term
Why is calculating the SE’s for the Bureau’s estimates a delicate business?
Definition
Due to the clusters in the sample. Each USU is a cluster. The simple random sample formulas ( with SD of Box etc ) do not apply to cluster samples.
Term
Which has more information : cluster sample or simple random sample? Why?
Definition
When size is same for both a simple random sample and a cluster sample, a simple random sample has more information. This is because in simple random sample, a person and his neighbor have remote chance of getting into the sample unlike in the cluster sample. A dad and son in a USU will give same information to the investigator.
Term
What is half-sample method? Why is it needed in the Current Population Survey sample?
Definition
A second sample will cost $40 million a year. So in stead of getting 2 samples, the Bureau splits the survey into 2 independent pieces that have the same chance behavior. Then takes the difference of the estimates and this serves as the SE. The pooled estimate of the two ( average of the two ) is taken as the estimate of the characteristic to be estimated.
Term
In the Survey which has a more accurate estimate :size of the labor force or number of unemployed as compared to simple random sample ?
Definition
Bureau’s SE for estimating the size of the labor force is 5% smaller than for a simple random sample, because weights are doing a good job.
Bureau’s SE for estimating the size of the unemployment is 50% worse than for a simple random sample, because the clustering hurts.
Term
What is the whole lesson from the design of the Current Population Survey sample?
Definition
To compute a standard error properly, you need more than the sample data; you need to know how the sample was picked. Recall that the sample for rhe Bereau’s work is done with clusters.
Term
Why does the bureau estimate the population percentage of the labor force with different weights to groups?
Definition
The sampling rate is different from stratum to stratum. If any group is over-represented in the sample than in the population, smaller weights are given to bring the sample back into line with the population. Same way for under-representation, a little increase in weight is made. Adjusting the weights helps correcting imbalances caused by chance variation and reducing sampling error.
Term
Why survey data are considered as more accurate than census data?
Definition
Unlike census the Current Population Surveys operate on a much smaller scale. Also there is careful selection, training, and supervision of the field staff. About 3% of the monthly sample is re-interviewed by the supervisors. The interviewer’s reports are checked for incomplete or inconsistent entries.
Term
Is it possible to look at the data and detect bias when it operates evenly across the sample?
Definition
No. SE’s computed by the half-sample method will not pick up this kind of bias.
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