Completion Rates and Panel Attrition
Completion rates for the ALP are high, generally in the 70 percent range. These rates can vary by subgroup, how long a survey is kept in the field, the number of reminders sent, interview topic, survey length, the amount of the incentive, and other factors. The completion rate for a given survey is calculated by dividing the number of completed interviews by the number of panel members invited to take that survey. Most ALP members complete an interview within one week of receiving the invitation and almost all do so within two weeks.
Once in the ALP, participants tend to remain indefinitely, leading to low attrition rates. Over the past decade, annual attrition rates of the ALP are in the range of 6 to 15%. To calculate attrition rates, we calculate the proportion of "active" panel members at a base period and compare it with a later time period. An "active" panel member has completed at least one survey in the past year as well as updated her/his demographic information within the past year.
Mathematically, the attrition rate is the difference between (a) and (b) divided by (a) or (a-b)/a. ALP attrition rates by year since 2006 are in the last column of the table below.
|Base year||Comparison year||Active in base period||Active in comparison period||% active||% attrition|
This table shows attrition for 2006 in 2007 was 15 percent. That is, of the 341 active respondents in 2006, 51 (or 341 less 290), or 15 percent, were no longer active in 2007. Similarly, it shows an attrition rate of 11 percent for 2007 respondents in 2008. The attrition rates have been between 6 and 15 percent annually.
Panel members generally do not give notice about their intent to leave the panel; rather, they simply stop participating in surveys. To avoid retention of disinterested panel members, RAND periodically attempts to contact members who have not been active for more than a year removes from the panel those who no longer wish to take part or cannot be contacted.