The Effect of Incentives on Internet Surveys: Response Rate Changes After the Introduction of Incentives

Incentives are often included in survey design because they are known to improve response rates, at least moderately. This paper describes the changes in the response rates when incentives were introduced into a longitudinal survey. The National Survey of Student Engagement was conducted annually at Indiana University Bloomington from 2000 through 2012. In 2010, incentives were introduced in an attempt to reverse the declining response rates. The incentives performed as expected, raising the AAPOR Response Rate 3 from 24% in 2009 to 36% in 2010. From 2010 through 2012, different types of incentives were tried but the response rates did not change substantially. The results from the changes in incentives can help survey practitioners decide the number and types of incentives that might be used effectively to increase response rates

Reduced Hepatic Synthesis of Calcidiol in Uremia

Calcidiol insufficiency is highly prevalent in chronic kidney disease (CKD), but the reasons for this are incompletely understood. CKD associates with a decrease in liver cytochrome P450 (CYP450) enzymes, and specific CYP450 isoforms mediate vitamin D3 C-25-hydroxylation, which forms calcidiol. Abnormal levels of parathyroid hormone (PTH), which also modulates liver CYP450, could also contribute to the decrease in liver CYP450 associated with CKD. Here, we evaluated the effects of PTH and uremia on liver CYP450 isoforms involved in calcidiol synthesis in rats. Uremic rats had 52% lower concentrations of serum calcidiol than control rats (P < 0.002). Compared with controls, uremic rats produced 71% less calcidiol and 48% less calcitriol after the administration of vitamin D3 or 1α-hydroxyvitamin D3, respectively, suggesting impaired C-25-hydroxylation of vitamin D3. Furthermore, uremia associated with a reduction of liver CYP2C11, 2J3, 3A2, and 27A1. Parathyroidectomy prevented the uremia-associated decreases in calcidiol and liver CYP450 isoforms. In conclusion, these data suggest that uremia decreases calcidiol synthesis secondary to a PTH-mediated reduction in liver CYP450 isoforms