Measuring numeracy without a math test: development of the subjective numeracy scale (SNS).
Fagerlin A, Zikmund-Fisher BJ, Ubel PA, Jankovic A, Derry HA, Smith DM. Medical Decision Making. 27:672-680, 2007.

What is perfect health to an 85 year-old? Evidence for scale recalibration in subjective health ratings.
Ubel PA, Jankovic A, Smith DM, Langa K, Fagerlin A. Medical Care. 43:1054-1057, 2005.