Subject selection

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

3. Problems • Explanation • Opinion and behavior • Five-point scale

4. Five-point scale 1 = 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.

5. SELECTING SUBJECTS • Three basic random sampling techniques • simple random sampling • systematic random sampling • stratified random sampling

6. Simple random sampling With 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.

7. 01 Beijing University 11 Liaoning Normal University02 Qinghua University 12 Sichuan University03 Beijing Normal University 13 Wuhan University04 Fudan University 14 Nankai University05 Huadong Normal University 15 Zhongshan University06 Nanjing Normal University 16 Henan University07 Shanghai University 17 Shantou University08 Dongnan University 18 Zhejiang University09 Nanjing University 19 Shangdong University10 Hehai University 20 Xiamen University Table 6.4: Numbered population of 20 universities

8. Task One Select 10 universities out of the 20 universities

9. A brief table of random numbers 9156742595279583013404024863852988099730 4650318584188454961802304510382065558727 3491463976887208276534476170328758940836 574911670323167493234502133132 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

10. 01 Beijing University11 Liaoning Normal University02 Qinghua University12 Sichuan University03 Beijing Normal University13 Wuhan University04 Fudan University14 Nankai University05 Huadong Normal University15 Zhongshan University06 Nanjing Normal University16 Henan University07 Shanghai University17 Shantou University08 Dongnan University18 Zhejiang University09 Nanjing University19 Shangdong University10 Hehai University20 Xiamen University 01, 02, 04, 09, 10, 18, 20,11, 03, 16

11. Systematic random sampling Why 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.

12. A brief table of random numbers 915674259527958 3013404024863852988099730 465031858418845496180230451038 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

13. 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

14. A brief table of random numbers 9156742595 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

15. 674+30=704 674, 704, 734, 764, 794, 824, 854, 884, 14, 44, 74, 104, 134, 164, 194, 224, 254, 284, 314, 344, 374, 404, 434, 464, 494, 524, 554, 584, 614, 644

16. 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%.

17. Procedures for stratified-random sampling • Divide the students into subpopulations • Extract a random sample from each subpopulation by a systematic random sampling.

18. 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

19. 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

20. A brief table of random numbers 9156742595 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

21. 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 56, 62, 68, 74, 80, 86, 92-90=2, 8, 12, 18, 24, 30, 36, 40, 46

22. A brief table of random numbers 9156742595 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

23. 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=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

24. Convenience sampling Despite 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.

25. 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?

26. 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.

27. 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.

28. 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.

29. 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.

30. 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?

31. 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

32. 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?

33. 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.