Development and validation of a measure of health literacy in the UK: the newest vital sign

BACKGROUND Health literacy (HL) is an important public health issue. Current measures have drawbacks in length and/or acceptability. The US-developed Newest Vital Sign (NVS) health literacy instrument measures both reading comprehension and numeracy skills using a nutrition label, takes 3 minutes to administer, and has proven to be acceptable to research subjects. This study aimed to amend and validate it for the UK population. METHODS We used a three-stage process; (1) a Delphi study with academic and clinical experts to amend the NVS label to reflect UK nutrition labeling (2) community-based cognitive testing to assess and improve ease of understanding and acceptability of the test (3) validation of the NVS-UK against an accepted standard test of health literacy, the Test of Functional Health Literacy in Adults (TOFHLA) (Pearson's r and the area under the Receiver Operating Characteristic (ROC) curve) and participant educational level. A sample size calculation indicated that 250 participants would be required. Inclusion criteria were age 18-75 years and ability to converse in English. We excluded people working in the health field and those with impaired vision or inability to undertake the interview due to cognitive impairment or inability to converse in English. RESULTS In the Delphi study, 28 experts reached consensus (3 cycles). Cognitive testing (80 participants) yielded an instrument that needed no further refinement. Validation testing (337 participants) showed high internal consistency (Cronbach's Alpha = 0.74). Validation against the TOFHLA demonstrated a Pearson's r of 0.49 and an area under the ROC curve of 0.81. CONCLUSIONS The NVS-UK is a valid measure of HL. Its acceptability and ease of application makes it an ideal tool for use in the UK. It has potential uses in public health research including epidemiological surveys and randomized controlled trials, and in enabling practitioners to tailor care to patient need.