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Research Assistant: For Students: Purpose Statement
This site gives advice on how to write an effective purpose (thesis) statement. The summary is given as answers to four questions: what? why? when? how?.
San Jose State University
San Jose State: Writing a Winning Statement of Purpose [Pdf]
How do you write a winning statement of purpose? This is a clear and comprehensive explanation of how to approach and write an essay from the San Jose State University. Practice exercises are given at the end.