The SRS Summary Arrests by Ethnicity and Age report as compared with the similar SRS Summary Arrests by Race and Age may appear to have lower counts, which suggests one or the other is presenting incorrect information. This is not the case. Rather, some information that the ethnicity report relies upon is lost when converting NIBRS to Summary data.
When converting NIBRS to Summary information to provide standardized data on which to report, Crime Insight conforms to the FBI specification for Summary data. This means that only the H and N values are stored for ethnicity. When the NIBRS data specifies a value other than that represented by H or N, the ethnicity is recorded as Unknown.
"Data Element 50 (Ethnicity [of Arrestee])—entry of H or N"
Crime Insight doesn't count arrestees by ethnicity if the ethnicity is unknown or missing so the ethnicity counts are always potentially lower.