Cohen, Louis. <br/><br/>
Research methods in education / 
Louis Cohen and Lawrence Manion. 
 - 4th edition. 
 - London :  Routledge,  c1994. 
 - 414 pages ;  23 cm. 
<br/><br/> Includes bibliographical references and index. 
<br/><br/><label>ISBN: </label>0415102359