Which is the correct statistical test to use?

References 

1. Bland M. An introduction to medical statistics. 3rd ed.. Oxford University Press; 2000;
2. The Statistics Homepage http://www.statsoft.com/textbook/stathome.html.
3. Siegel S. Nonparametric statistics for the behavioral sciences. 2nd ed.. London: McGraw-Hill; 1988;
4. Pallant J. SPSS survival manual. 2nd ed.. Maidenhead: Open University Press; 2005;
5. Interactive Statistical Calculation Pages http://www.statpages.org/#Power.
6. Laverick S, Lowe D, Brown JS, Vaughan ED, Rogers SN. The impact of neck dissection on health-related quality of life. Arch Otolaryngol Head Neck Surg. 2004;130:149–154http://archotol.ama-assn.org/cgi/reprint/130/2/149.pdf
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