sampling obtaining a sample from a population. a population is all the people or objects of interest...
TRANSCRIPT
![Page 1: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/1.jpg)
SAMPLING
Obtaining a Sample From a Population
![Page 2: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/2.jpg)
A population is all the people or objects ofinterest in a study.
![Page 3: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/3.jpg)
![Page 4: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/4.jpg)
The population for a study about UNI studentsis all the students at UNI.
![Page 5: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/5.jpg)
If a study utilized everyone in a population,the sample would be called a
Census.
![Page 6: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/6.jpg)
A CENSUS is a sample of an entire Population….
They are seldom done because…..
![Page 7: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/7.jpg)
A CENSUS is a sample of an entire Population….
They are seldom done because…..
1. Impossible
![Page 8: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/8.jpg)
![Page 9: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/9.jpg)
A CENSUS is a sample of an entire Population….
They are seldom done because…..
1. Impossible2. Unprofitable
![Page 10: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/10.jpg)
A CENSUS is a sample of an entire Population….
They are seldom done because…..
1. Impossible2. Unprofitable3. Less accurate
![Page 11: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/11.jpg)
So… instead of a census,a sample is taken.
![Page 12: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/12.jpg)
![Page 13: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/13.jpg)
Sampling is the process of discovering what a populationis like….. but
You can never look directly at the population!
![Page 14: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/14.jpg)
The population is like a large container… you can pull things outbut you are NEVER allowed to look at all its contents.
![Page 15: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/15.jpg)
Sampling must be done properly orsampling itself can invalidate your research!
![Page 16: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/16.jpg)
Sampling is a five step process:
![Page 17: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/17.jpg)
Sampling is a five step process
Each step is important
5
![Page 18: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/18.jpg)
Sampling is a five step processEach step is important
Or the sample will not givean accurate estimate of the
population.
![Page 19: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/19.jpg)
1.Before a sample can be taken from a population: that population must be defined.
![Page 20: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/20.jpg)
1. Before a sample can be taken from a population that population must be defined.
A population: The total member of objects orpersons that are of interest for a study.
Male Female Male Female
France India
![Page 21: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/21.jpg)
1. Before a sample can be taken from a population that population must be defined.
A population: The total member of objects orpersons that are of interest for a study.
The characteristics of a population are called:
Parameters.
![Page 22: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/22.jpg)
2. Identify the sampling frame
![Page 23: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/23.jpg)
2. Identify the sampling frame
A sampling frame is a list of the units of apopulation:
telephone numbersaddressesemail addresses
![Page 24: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/24.jpg)
![Page 25: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/25.jpg)
3. Select a sampling procedure
![Page 26: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/26.jpg)
3. Select a sampling procedure
Two kinds:1. Nonprobability samples2. Probability samples
![Page 27: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/27.jpg)
3. Select a sampling procedure
1. Nonprobability samples
![Page 28: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/28.jpg)
3. Select a sampling procedure
1. Nonprobability samplesConvenience Sample (Accidental Sample)
![Page 29: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/29.jpg)
3. Select a sampling procedure
1. Nonprobability samplesConvenience Sample (Accidental Sample)
Judgmental Sample
![Page 30: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/30.jpg)
3. Select a sampling procedure
1. Nonprobability samplesConvenience Sample (Accidental Sample)
Judgmental SampleQuota sample
![Page 31: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/31.jpg)
![Page 32: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/32.jpg)
3. Select a sampling procedure
2. Probability samples
![Page 33: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/33.jpg)
3. Select a sampling procedure
2. Probability samplesSimple Random Sample (SRS)
![Page 34: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/34.jpg)
3. Select a sampling procedure
2. Probability samplesSimple Random Sample (SRS)
Special case of the convenience sample…..
![Page 35: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/35.jpg)
3. Select a sampling procedure
2. Probability samplesSimple Random Sample (SRS)
Stratified Sample
![Page 36: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/36.jpg)
![Page 37: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/37.jpg)
3. Select a sampling procedure
2. Probability samplesSimple Random Sample (SRS)
Stratified SampleCluster Sample
![Page 38: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/38.jpg)
Cluster Sample
![Page 39: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/39.jpg)
3. Select a sampling procedure
2. Probability samplesSimple Random Sample (SRS)
Stratified SampleCluster SampleSystematic Sample
![Page 40: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/40.jpg)
Note: Important!
The human mind will not randomize!
![Page 41: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/41.jpg)
4. Determine a sample size
![Page 42: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/42.jpg)
4. Determine a sample size
What is the correct sample size?
The answer is always the same.
IT DEPENDS!
![Page 43: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/43.jpg)
4. Determine a sample size
And what does it depend upon?
![Page 44: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/44.jpg)
4. Determine a sample size
And what does it depend upon? 1. Sampling error
http://www.rasmussenreports.com/public_content/politics/obama_administration/daily_presidential_tracking_poll
![Page 45: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/45.jpg)
4. Determine a sample size
And what does it depend upon? 1. Sampling error
National Survey of 1,000 Likely VotersConducted September 20-21, 2010By Rasmussen Reports 1* Is the current structure of the Social Security system a Ponzi scheme? 27% Yes36% No37% Not sure
NOTE: Margin of Sampling Error, +/- 3 percentage points with a 95% level of confidence
![Page 46: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/46.jpg)
4. Determine a sample size
And what does it depend upon? 1. Sampling error2. Precision
![Page 47: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/47.jpg)
4. Determine a sample size
And what does it depend upon? 1. Sampling error2. Precision3. Degree of confidence
![Page 48: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/48.jpg)
4. Determine a sample size
And what does it depend upon? 1. Sampling error2. Precision3. Degree of confidence4. Other factors
a. timeb. costc. type of scalesd. number of cross-classifications
![Page 49: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/49.jpg)
4. Determine a sample size
And what does it depend upon? 1. Sampling error2. Precision3. Degree of confidence4. Other factors
f. historical and secondary datag. statistical considerationsh. political considerations
![Page 50: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/50.jpg)
4. Determine a sample size
Since any given interval on the normal curve can be calculated by:
HZ
n
![Page 51: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/51.jpg)
4. Determine a sample size
Since any given interval on the normal curve can be calculated by:
HZ
n
x
xxZ
![Page 52: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/52.jpg)
HZ
n
H = Z SE
SEn
nZ
H
2 2
2
![Page 53: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/53.jpg)
Since any given interval on the normal curve can be calculated by:
HZ
n
The sample size can then be seen as:
nZ
H
2 2
2
![Page 54: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/54.jpg)
The sample size for nominal and ordinal datacan then be seen as:
nZ pq
H
2
2
![Page 55: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/55.jpg)
H Zpq
n
H = ZSE
SEpq
n
nZ pq
H
2
2
![Page 56: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/56.jpg)
What size sample would be needed if you wished to make a decision to within 2 IQ point with 95% accuracy?
IQ has a standard deviation of 15…… therefore:n
Z
H
2 2
2
With Z = 2, H = 2; therefore….
nZ
H
2 2
2
2 15
2225
2 2
2
![Page 57: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/57.jpg)
It is assumed that 55% of all students are women, what size sample would beneeded to test this assumption to a 95% accuracy at 2%?
nZ pq
H
2
2
p = .55, q = .45 (p + q = 1); H = .02; Z = 2
n 2 55 45
022475
2
2
(. )( . )
(. )
![Page 58: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/58.jpg)
The largest sample size that will ever be needed for any given H is when nominal data is beingused and p = q = 0.5. Therefore the largest sampleEVER needed is:
nH
12
![Page 59: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/59.jpg)
What size sample would be needed to:
1. Use a GPA scale with a SD = 15 to an accuracy of 95% at 3 IQ points?
![Page 60: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/60.jpg)
What size sample would be needed to:
1. Use a GPA scale with a SD = 15 to an accuracy of 95% at 3 IQ points?
2. A Likert scale to a 95% accuracy of 0.4?
![Page 61: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/61.jpg)
What size sample would be needed to:
1. Use a GPA scale with a SD = 15 to an accuracy of 95% at 3 IQ points?
2. A Likert scale to a 95% accuracy of 0.4?
3. Income scale with a SD = $15,000 to within a 95% accuracy of $5,000?
![Page 62: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/62.jpg)
What size sample would be needed to:
1. Use a GPA scale with a SD = 15 to an accuracy of 95% at 3 IQ points?
2. A Likert scale to a 95% accuracy of 0.4?
3. Income scale with a SD = $15,000 to within a 95% accuracy of $5,000?
4. The largest sample that would ever be needed to do an over-night politicalpoll with a 95% accuracy of 2%?
![Page 63: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/63.jpg)
What size sample would be needed to:
1. Use a GPA scale with a SD = 15 to an accuracy of 95% at 3 IQ points?
2. A Likert scale to a 95% accuracy of 0.4?
3. Income scale with a SD = $15,000 to within a 95% accuracy of $5,000?
4. The largest sample that would ever be needed to do an over-night politicalpoll with a 95% accuracy of 2%?
5. To test a hypothesis that 80% of all customers will buy a product again to within 95% accuracy at 3%?
![Page 64: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/64.jpg)
National Survey of 1,000 Likely VotersConducted September 20-21, 2010By Rasmussen Reports 1* Is the current structure of the Social Security system a Ponzi scheme? 27% Yes36% No37% Not sure
NOTE: Margin of Sampling Error, +/- 3 percentage points with a 95% level of confidence
Why is it +/- 3 percent at 95% confidence?
What is the sample size?
![Page 65: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/65.jpg)
4. Determine a sample size
What about the size of the population?
![Page 66: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/66.jpg)
4. Determine a sample size
What about the size of the population?
Does that change the size of the sampleneeded?
![Page 67: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/67.jpg)
4. Determine a sample size
Surprisingly so,
Usually not!!
![Page 68: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/68.jpg)
4. Determine a sample size
Pragmatically, the sample size is independentof the population size!
Except for very small populations, or very, very large samples.
![Page 69: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/69.jpg)
5. Collect data (go do it!!)
![Page 70: SAMPLING Obtaining a Sample From a Population. A population is all the people or objects of interest in a study](https://reader035.vdocuments.us/reader035/viewer/2022062222/5697bfeb1a28abf838cb813f/html5/thumbnails/70.jpg)
An example of the problems in samplingand the value of demographics….
http://www.dailymail.co.uk/news/article-1315078/Race-maps-America.html
http://www.prb.org/Publications/Articles/2008/workingaroundtheclock.aspx