NORC I 2016 VSP Summary Data Report for the vision& Eye Health Surveillance System Data is analyzed on an annual basis The development of this algorithm was based on the practices of the CMS Chronic Conditions Warehouse reporting system, feed back from project partners and experts, as well as the results of a literature review intended to identify normal and best practices for prevalence reporting from administrative data sources This literature review is included in Appendix A of the"Claims registry Analysis Plan"report Diagnosis Categories and Subgroup Indicators Medical Diagnoses are reported based on the VEHSS-defined medical diagnosis categorization structure As reported in detail in the VEHSS Medical Diagnosis Categorization Report, we identified all eye and vision related ICD9 and ICD10 diagnosis codes, and organized them into a 2-level categorization structure which has 17 Categories and 79 Subgroups(Table 4) For example, assume a beneficiary has 3 eye and vision related ICD9 codes in the year of observation 362.3 Retinal vascular occlusion, unspecified 3629 Retinal nerve fiber bundle defects 362. 11 Hypertensive retinopathy 362.3 and 362.9 are both assigned to subgroup ' Retina vascular disease, Occlusive(arterial, venous) 362. 11 is assigned to a different subgroup; Retina vascular disease, Non-Occlusive. Both of these subgroups are within one category(Other Retinal Disorders This beneficiary is counted as one prevalent case for subgroup Retina vascular disease, Occlusive (arterial, venous), and one case for subgroup ' Retina vascular disease, Non-Occlusive. This beneficiary would count as one case in the category "Other Retinal Disorders. Thus, individual patients can appear in multiple subgroups, but cannot be double counted within a specific category or subgroup. Patients may also appear in multiple separate categories Denominator used to calculate prevalence rates The patient population( denominator) includes those who were enrolled in VSP at any time during the calendar year. VSP enrollment data is based primarily on employer-provided enrollment data, and may not accurately reflect the actual number of patients enrolled in VSP over the course of the year. In addition, some patient enrollment data is incomplete, with 8%of enrollees not having a state of residenceNORC | 2016 VSP Summary Data Report for the Vision & Eye Health Surveillance System 9 ■ Data is analyzed on an annual basis. The development of this algorithm was based on the practices of the CMS Chronic Conditions Warehouse reporting system, feedback from project partners and experts, as well as the results of a literature review intended to identify normal and best practices for prevalence reporting from administrative data sources. This literature review is included in Appendix A of the “Claims & Registry Analysis Plan” report. Diagnosis Categories and Subgroup Indicators Medical Diagnoses are reported based on the VEHSS-defined medical diagnosis categorization structure. As reported in detail in the VEHSS Medical Diagnosis Categorization Report, we identified all eye and vision related ICD9 and ICD10 diagnosis codes, and organized them into a 2-level categorization structure which has 17 Categories and 79 Subgroups (Table 4). For example, assume a beneficiary has 3 eye and vision related ICD9 codes in the year of observation: ■ 362.3 Retinal vascular occlusion, unspecified ■ 362.9 Retinal nerve fiber bundle defects ■ 362.11 Hypertensive retinopathy 362.3 and 362.9 are both assigned to subgroup ‘Retina vascular disease, Occlusive (arterial, venous)’. 362.11 is assigned to a different subgroup; ‘Retina vascular disease, Non-Occlusive’. Both of these subgroups are within one category (Other Retinal Disorders). This beneficiary is counted as one prevalent case for subgroup ‘Retina vascular disease, Occlusive (arterial, venous)’, and one case for subgroup ‘Retina vascular disease, Non-Occlusive’. This beneficiary would count as one case in the category ‘Other Retinal Disorders’. Thus, individual patients can appear in multiple subgroups, but cannot be double counted within a specific category or subgroup. Patients may also appear in multiple separate categories. Denominator used to Calculate Prevalence Rates The patient population (denominator) includes those who were enrolled in VSP at any time during the calendar year. VSP enrollment data is based primarily on employer-provided enrollment data, and may not accurately reflect the actual number of patients enrolled in VSP over the course of the year. In addition, some patient enrollment data is incomplete, with 8% of enrollees not having a state of residence on file