Imputation accuracy heat map for the Han Chinese and European populations with 24 population-specific reference panels. The colors that changed from light blue to red represented the imputation accuracy (measured by EmpR²). The x-axis represented the 24 population-specific reference panels from the 1000G Phase 3. The y-axis represented the four different haplotype sizes of reference panels. The without asterisk marked group (upper) was for the Han Chinese population, and the asterisk marked group (lower) was for the European population.