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Transcript of 1 Subject selection 2 Perceptual learning styles Visual learning 3, 4, 7, 17, 20 Auditory...
1
Subject selection
2
Perceptual learning styles
Visual learning
3, 4, 7, 17, 20
Auditory learning
1, 6, 9,13, 15
Tactile learning
8, 10, 12, 16, 18
Kinesthetic learning
2, 5, 11, 14, 19
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Problems
Explanation Opinion and behavior Five-point scale
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Five-point scale1 = This statement is never or almost
never true of me.
2 = This statement is usually not true of me.
3 = This statement is somewhat true of me.
4 = This statement is usually true of me.
5 = This statement is completely or almost completely true of me.
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SELECTING SUBJECTS
Three basic random sampling techniques
simple random sampling
systematic random sampling
stratified random sampling
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Simple random samplingWith simple random sampling, each
unit is numbered from 1 to N (where N
is the size of the population). Next, a
table of random numbers is used to
select n items to the sample.
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01 Beijing University 11 Liaoning Normal University
02 Qinghua University 12 Sichuan University
03 Beijing Normal University 13 Wuhan University
04 Fudan University 14 Nankai University
05 Huadong Normal University 15 Zhongshan University
06 Nanjing Normal University 16 Henan University
07 Shanghai University 17 Shantou University
08 Dongnan University 18 Zhejiang University
09 Nanjing University 19 Shangdong University
10 Hehai University 20 Xiamen University
Table 6.4: Numbered population of 20 universities
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Task One
Select 10 universities out of the 20
universities
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A brief table of random numbers
91567 4259527958301340402486385298809973046503 1858418845496180230451038206555872734914 6397688720827653447617032875894083657491 1670323167493234502133132 12544 41035
30405 83946 23792 14422 15059 45799 22716 19792
09983 74353 68668 30429 70735 25499 16631 35006
85900 07119 97336 71048 08178 77233 13916 47564
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01 Beijing University 11 Liaoning Normal University
02 Qinghua University 12 Sichuan University
03 Beijing Normal University 13 Wuhan University
04 Fudan University 14 Nankai University
05 Huadong Normal University 15 Zhongshan University
06 Nanjing Normal University 16 Henan University
07 Shanghai University 17 Shantou University
08 Dongnan University 18 Zhejiang University
09 Nanjing University 19 Shangdong University
10 Hehai University 20 Xiamen University
01, 02, 04, 09, 10, 18, 20,11, 03, 16
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Systematic random samplingWhy do we need systematic random sampling?Suppose the total number of a population consists of 900 students and you would like to select 30 students out of them as a random sample. Following the technique of simple random sampling, you need to spend a lot of time.
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A brief table of random numbers
91567 42595 27958 301340402486385298809973046503 185841884549618 02304 51038 20655 58727
34914 63976 88720 82765 34476 17032 87589 40836
57491 16703 23167 49323 45021 33132 12544 41035
30405 83946 23792 14422 15059 45799 22716 19792
09983 74353 68668 30429 70735 25499 16631 35006
85900 07119 97336 71048 08178 77233 13916 47564
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Procedures for systematic random sampling
Number all the subjects. Calculate the interval
The total number of the populationInterval =
The size of the sample
Choose the number to start with
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A brief table of random numbers
91567 42595 27958 30134 04024 86385 29880 99730
46503 18584 18845 49618 02304 51038 20655 58727
34914 63976 88720 82765 34476 17032 87589 40836
57491 16703 23167 49323 45021 33132 12544 41035
30405 83946 23792 14422 15059 45799 22716 19792
09983 74353 68668 30429 70735 25499 16631 35006
85900 07119 97336 71048 08178 77233 13916 47564
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674+30=704
674, 704, 734, 764, 794, 824, 854, 884, 14, 4
4, 74, 104, 134, 164, 194, 224, 254, 284, 314,
344, 374, 404, 434, 464, 494, 524, 554, 584, 6
14, 644
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Stratified-random sampling
Why do we need stratified-random sampling?
Suppose there are 900 first-year students majoring in science in one national university. Among them, there are only 90 female students. Suppose you want to get a sample of 30 students in which males and females are balanced. If using systematic random sampling, the female students may be far less than 10%.
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Procedures for stratified-random sampling
• Divide the students into subpopulations
• Extract a random sample from each
subpopulation by a systematic random
sampling.
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Procedures for systematic random sampling
Number all the subjects. Calculate the interval
The total number of the population
Interval =
The size of the sample
Choose the number to start with
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Task Three
Select a sample of 30 students out of the 900 students with males and females being evenly divided.
– Females: 90; males: 810– 15 out of the 90; 15 out of the 810 by a
systematic random sampling
90/15=6; 810/15=54
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A brief table of random numbers
91567 42595 27958 30134 04024 86385 29880 99730
46503 18584 18845 49618 02304 51038 20655 58727
34914 63976 88720 82765 34476 17032 87589 40836
57491 16703 23167 49323 45021 33132 12544 41035
30405 83946 23792 14422 15059 45799 22716 19792
09983 74353 68668 30429 70735 25499 16631 35006
85900 07119 97336 71048 08178 77233 13916 47564
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Task ThreeSelect a sample of 30 students out of the 900 students with males and females being evenly divided.
– Females: 90; males: 810
– 15 out of the 90; 15 out of the 810 by a
systematic random sampling
90/15=6; 810/15=54
56, 62, 68, 74, 80, 86, 92-90=2, 8, 12,
18, 24, 30, 36, 40, 46
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A brief table of random numbers
91567 42595 27958 30134 04024 86385 29880 99730
46503 18584 18845 49618 02304 51038 20655 58727
34914 63976 88720 82765 34476 17032 87589 40836
57491 16703 23167 49323 45021 33132 12544 41035
30405 83946 23792 14422 15059 45799 22716 19792
09983 74353 68668 30429 70735 25499 16631 35006
85900 07119 97336 71048 08178 77233 13916 47564
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Task ThreeSelect a sample of 30 students out of the 900 students with males and females being evenly divided.
–Females: 90; males: 810–15 out of the 90; 15 out of the 810 by a
systematic random sampling
90/15=16; 810/15=54
F: 56, 72, 88, 104-90=14, 30, 46, 62, 78, 94-90=4
20, 36, 52, 68, 84, 100-90=10
M: 674, 728, 782, 836-810=26, 80, 134, 188, 242,
296, 350, 404, 458, 512, 566, 620
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Convenience samplingDespite our best efforts, it is often impossible to do
strict random sampling in our actual research
especially for individual researchers. Often,
instead of strict random sampling techniques, we
simply use convenience sampling, i.e. elements are
selected for the sample for the convenience of the
researcher. In other words, the researcher tends
to choose subjects that are readily available.
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What needs to be considered in subject selection?
• A large sample size or a relatively small one?
• A random sample or a convenience sample?
• Longitudinal or cross-sectional?
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A large sample size or a relatively small one?
Based on my understanding of the statistical
requirement, the smallest sample for a
survey is no less than 30 while a large
sample, is no less than 500. If your study
needs to compare two or three groups, then
each group requires to be no less than 30.
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A random sample or a convenience sample?
• As a graduate student, you more often
than not cannot obtain a random sample
due to many practical constraints.
• For a convenience sample, you need to
decide on the procedures by which the
subjects are chosen.
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For example, is your sample obtained on a voluntary-basis or based on the subjects’ L2 proficiency levels or through the teachers’ recommendation? Obviously, the subjects who voluntarily join the study won’t have any cooperation problem in data-collection but may be less representative because the students who volunteer are likely to be among the more motivated ones. Taking an intact class as a sample will be better than the volunteers if you want the study to be more generalizable.
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Longitudinal or cross-sectional?• If a study is to detect changes or reveal
developmental patterns in certain variables, then the subjects need to be studied at several points of time. In this case, the subjects form a longitudinal sample.
• However, sometimes, the researcher cannot afford the time to follow up the same group of subjects for several years, you choose a cross-sectional sample in which the subjects who are selected from Year One through Year Four are studied only once.
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Decide which random sampling technique will be better used in the following study:
In 1999, 180 students were enrolled in the School of Foreign Studies at Nanjing University. Among them, 70 were majoring in English, 25 in French, 24 in German, 26 in Japanese, 20 in Russian and 15 in Spanish. How can we get a representative sample of 30 to represent the 180 students?
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English: 30 x 70/180 = 30x0.39 12
French: 30 x 25/180 = 30x 0.14 4
German: 30 x 24/180 = 30x0.13 4
Japanese: 30 x 26/180 =30x0.14 4
Russian: 30 x 20/180 = 30x0.11 3
Spanish: 30 x 15/180 = 30x0.08 2
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English: 70 x 30 /180 = 70x0.17 12
French: 25 x 30/180 = 25x0.17 4
German: 24 x 30/180 =24x0.17 4
Japanese:26 x 30/180 =26x0.17 4
Russian: 20 x 30/180 = 20x0.17 3
Spanish: 15 x 30/180 = 15x0.17 2
29?
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Homework • Try to examine the internal validity of items in the
questionnaire given and try to revise it. Next week, we will have a discussion on the questionnaire in a small class.
• Construct a questionnaire to answer your own research question. In addition to a complete questionnaire, you should also include the following information:
– one research question; what kind of information you would like to obtain; what kind of scaling techniques you would like to employ; what categories you plan to have.
– Please bring 6 copies to class next week.