Should Health Numeracy Be Assessed Objectively or Subjectively?

INTRODUCTION: Because current evidence suggests that numeracy affects how people make decisions, it is an important factor to account for in studies assessing the effectiveness of medical decision support interventions. Subjective and objective numeracy assessment methods are available that vary in theoretical background, skills assessed, known relationship with decision making skills, and ease of implementation. The best way to use these tools to assess numeracy when conducting medical decision-making research is currently unknown.
METHODS: We conducted Internet surveys comparing numeracy assessments obtained using the subjective numeracy scale (SNS) and 5 objective numeracy scales. Each study participant completed the SNS and 1 objective numeracy measure. Following each assessment, participants indicated willingness to repeat the assessment and rated its user acceptability.
RESULTS: The overall response rate was 78%, resulting in a total sample size of 673. Spearman correlations between the SNS and the objective numeracy measures ranged from 0.19 to 0.44. Acceptability assessments for the short form of the Numeracy Understanding in Medicine Instrument and the SNS did not differ significantly. The other objective scales all had lower acceptability ratings than the SNS.
CONCLUSIONS: These findings are consistent with prior research suggesting that objective and subjective numeracy scales measure related but distinct constructs. Due to current uncertainty regarding which construct is more likely to influence the effectiveness of decision support interventions, these findings warrant further investigation to determine the proper use of objective versus subjective numeracy assessments in medical decision-making research. Pending additional information, a reasonable approach is to measure both objective and subjective numeracy so that the full range of actual and perceived numeracy skills can be taken into account.