The Caries Assessment Spectrum and Treatment (CAST) index: face and content validation

The aim of this study was to establish the face and content validity of the Caries Assessment Spectrum and Treatment (CAST) index. This hierarchical epidemiological index consists of 10 codes covering the spectrum of carious lesion progression and describing conditions ranging from the absence of carious lesions to the presence of sealants and restorations, the presence of lesions in enamel and dentine, and the presence of advanced stages of carious lesion in pulpal tissue and tissue surrounding the tooth.

Using the RAND modified e-Delphi consensus method, a set of 17 statements related to the content, including the codes and descriptions used, and suitability of the CAST index were scored on a scale of 1-9 by 15 senior epidemiologists from 15 countries over three rounds of assessment. Agreement of ≥ 75% was required to indicate consensus on a statement.

Consensus was reached on 14 statements in the first round, none in the second and on the remaining three statements in the third round. To obtain feedback on the initial validation of the index and to test its external validity, 41 epidemiologists from 24 countries were requested to assess the validated statements. Minor changes to 10 of the 17 statements' content and descriptions were suggested; this necessitated the resubmission of the modified CAST index to the original 15 epidemiologists. Consensus of ≥ 80% was reached on all 10 statements regarding codes and their descriptions.

After a total of four rounds with the panel members and one round with the feedback group, the CAST index was approved for face and content validity. External validity was obtained. The participating epidemiologists found the RAND modified e-Delphi consensus method to be a suitable instrument for reaching consensus.