Do to others what you want them to do to you

25 Aug 2011

Sample size in Quantitative studies

Is your sample size sufficient for your quantitative analysis? This is a question that a lot of doctoral researchers ask. I guess it depends on the type of analysis used. My PhD research looked at blog readers and I used Structural Equation Modelling (SEM) to analyse my data. I used the following to justify my sample size.
  • For factor analysis, according to Hair et al., (2010), a sample should preferably be more than 100 for factor analysis to proceed
  • However,  according to Tabachnick and Fidell (2007 p. 613), it should be higher than 300 cases, the number that is considered “comfortable”.
If you are doing SEM:
  • A ratio of ten responses per free parameters is required to obtain trustworthy estimates (Bentler and Chou, 1987).
  • Others suggest a rule of thumb of ten subjects per item in scale development, is prudent (Flynn and Pearcy 2001).
  • However, if data is found to violate multivariate normality assumptions, the number of respondents per estimated parameter increases to 15 (Bentler and Chou 1987; Hair, et al. 2006).
References:

BENTLER, P. M. & CHOU, C. P. (1987) Practical issues in structural modeling. Sociological Methods & Research, 16, 78.

FLYNN, L. & PEARCY, D. 2001. Four subtle sins in scale development: Some suggestions for strengthening the current paradigm. International Journal of Market Research  43: (4) 409-433.

HAIR, J. F., BLACK, W. C., BABIN, B. J. & ANDERSON, R. E. 2010. Multivariate Data Analysis: A Global Perspective, New Jersey, Pearson Prentice Hall.

TABACHNICK, B. G. & FIDELL, L. S. 2007. Using Multivariate Statistics (5th Ed.) New York, HarperCollins.

8 Aug 2011

Passed my Viva

I finally passed my PhD viva with minor corrections last Thursday (4th of August, 2011). My external examiner was Prof Amanda Broderick, Professor of Marketing & Deputy Dean (Queens Campus) of Durham Business School while my internal examiner was Dr. Scott Dacko, Associate Professor of Marketing & Strategic. Warwick Business School - two of the nicest people.

The journey was hard was it was well worth it in the end.

Read my blog post about it on the PhD Life blog "My Viva – Light at the end of the tunnel".