Cheng et al. BMC Public Health 2011, 11:380 http://www.biomedcentral.com/1471-2458/11/380 Results Geographic map and geographic distribution of drugs consumption Figure 1 illustrates the administrative division across 352 townships in Taiwan, including 5 major metropolitan areas, 2 secondary metropolitan areas, 206 rural areas, and 55 aboriginal townships. The pattern of drug consumption across townships indicated the highest utilization was of Group C fol- lowed by Group A, Group B, Group D, and Group O. (Table 1) Among all groups of drugs, variations in con- sumption by metropolitan areas were the largest in Hsinchu (COV = 100 to 119%), followed by Tainan (COV = 71 to 106%), rural township (COV = 55 to 102%) and aboriginal area (COV = 38 to 98%). We did not observe any significant difference in cardi- ovascular medication consumption between northern and southern areas: Group A (21.2 ± 33.6, 17.8 ± 40.5; p = 0.67), Group B (11.8 ± 17.2, 10.1 ± 17.5; p = 0.51), Group C (20.8 ± 34.9, 19.0 ± 38.3; p = 0.86), Group D (6.3 ± 10.9, 5.6 ± 13.5; p = 0.83) and Group O (1.5 ± 3.1, 1.5 ± 3.4; p = 0.70), respectively. LISA statistics for cardiovascular drugs Figure 2 displays plots of the LISA statistics for each class of cardiovascular drug utilization. The marked polygons indicated areas with significant spatial cluster- ing, while the blank polygons indicated areas with insig- nificant spatial clustering. There were wide variations in utilization of all drug classes across the 352 townships in Taiwan. From the first glimpse of the LISA figures, under-utilization appeared to be the predominant spatial pattern for car- diovascular disorders across all drug classes: the total number of high-high associations (hot spots) amounts to 35, while low-low associations (cold spots) reaches to 85. Such spatial variations carried three statistical mean- ings: (1) variations were non-random; (2) variations Page 4 of 9 were statistically significant; (3) variations exhibited effects of neighboring interactions. North-south discrepancy distribution Focusing on the west of Taiwan, where more than 97 percent of the population resides, patterns of drug use exhibited more high-high associations clustered in the southern (n = 30) than northern (n = 2) townships. Thus the southern region had higher-than-average utili- zation of cardiovascular drugs than other parts of Tai- wan. However, at the same time, the number of low-low associations also presented in southern (n = 42) more than northern areas (n = 33). Tables 2 summarizes the distribution of spatial asso- ciations for each drug class by the levels of urbanization. Among all drug classes, a large number of significant LISA statistics were observed in metropolitan areas fol- lowed by aboriginal, rural, and secondary metropolitan areas. Among those metropolitan areas, the significant LISA statistics were mostly observed in the southern townships such as Kaohsiung and Tainan city. In other words, with each prescription drug, more observations were correlated with their neighboring values, giving evi- dence of possible diffusion effects of drug use. By drug class, both Group C and Group D had the highest amount of diverse clusters across the country, followed by Group B, Group A, and Group O. Hot spot areas concentrated mostly in the Kaohsiung and rural areas among all drug classes (Table 2). In contrast, cold spot areas showed up in rural and aboriginal townships areas, accounting for a particularly high portion of group A, followed by group B, group C, group O, and group D. Discussion Our study showed a variability of cardiovascular pre- scription patterns with regard to geographic differences in Taiwan. The analysis of both HH and LL associations Table 1 The distribution of cardiovascular medications consumption by urbanicity, data presented as mean ± (SD)a Population (%) Group Ab Group B Group C Group D Group O Taipei-Keelung metropolitan area (N = 44) Taoyuan-Chungli metropolitan area (N = 12) Hsinchu secondary metropolitan Area (N = 10) Taichung-Changhwa metropolitan area (N = 18) Chiayi secondary metropolitan area (N = 4) Tainan metropolitan area (N = 14) Kaohsiung metropolitan area (N = 28) Rural townships area (N = 167) Aboriginal townships area (N = 55) Total (N = 352) 6,609,220 (29.4) 1,846,082 (8.2) 682,132 (3.0) 2,092,344 (9.3) 373,774 (1.7) 1,246,084 (5.5) 2,758,140 (12.2) 6,100,872 (27.1) 812,703 (3.6) 22,521,351 (100) 32.2 (42.0) 40.9 (79.5) 18.2 (15.9) 41.7 (60.3) 36.5 (42.8) 27.1 (26.7) 43.9 (94.0) 18.2 (18.2) 25.3 (26.5) 25.7 (40.8) 18.1 (22.1) 20.0 (34.9) 11.0 (9.2) 24.1 (33.2) 19.5 (19.6) 15.6 (14.6) 23.0 (37.8) 10.7 (10.4) 10.4 (10.6) 13.9 (19.1) 32.3 (43.4) 40.4 (72.0) 21.2 (18.4) 45.6 (71.5) 40.1 (49.5) 31.7 (32.9) 45.7 (82.5) 19.3 (21.1) 19.6 (22.7) 26.0 (40.3) 10.2 (12.8) 11.7 (23.9) 6.1 (5.7) 13.5 (20.6) 13.1 (17.6) 7.2 (7.4) 12.5 (24.6) 5.7 (7.8) 7.7 (9.5) 7.9 (12.7) 2.7 (4.7) 2.4 (2.8) 1.1 (1.1) 3.5 (4.4) 4.3 (5.9) 2.7 (3.8) 3.7 (4.5) 1.6 (2.9) 1.3 (3.4) 2.1 (3.6) a. Data presented as DDD/1000 inhabitants per day b. Group A, agents acting on the rennin-angiotensin system; Group B, beta blocking agents; Group C, calcium channel blockers; Group D, diuretics; Group O, antihypertensives