. 2004 Nov 10;4:31. doi: 10.1186/1472-6963-4-31
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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Figure 2.
Effect of pre-warning on final questionnaire response rates.