Butz, William P., <br/><br/>
Why collect retrospective data? / 
William P. Butz   
 - 12 pages ;  28 cm. 
 - The Rand paper series;  P-6715 .
 - The Rand paper series;  P-6715  .
<br/><br/><label>Subjects--Topical Terms: </label><br/>Demographic surveys.