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Table 2 Patient Characteristics Before Matching

From: Reducing selection bias in case-control studies from rare disease registries

  Patients with Avascular Necrosis Patients without Avascular Necrosis Odds Ratio 95% Confidence Interval
Before Matching 853 4127   
Gender, n (%)     
Male 423 (49·6) 1899 (46·0) Reference*  
Female 430 (50·4) 2228 (54·0) 0·89 (0·78, 1·02)
Year of Birth, n (%)     
1910 - < 1920 4 (0·5) 34 (0·8) 0·49 (0·18, 1·31)
1920 - < 1930 21 (2·5) 125 (3·0) 0·66 (0·42, 1·05)
1930 - < 1940 75 (8·8) 198 (4·8) 1·27 (0·96, 1·68)
1940 - < 1950 114 (13·4) 384 (9·3) 1·06 (0·83, 1·35)
1950 - < 1960 146 (17·1) 529 (12·8) Reference*  
1960 - < 1970 147 (17·2) 590 (14·3) 0·92 (0·73, 1·16)
1970 - < 1980 156 (18·3) 665 (16·1) 0·88 (0·70, 1·10)
1980 - < 1990 129 (15·1) 659 (16·0) 0·76 (0·60, 0·96)
1990 - < 2000 58 (6·8) 633 (15·3) 0·39 (0·29, 0·53)
2000 - < 2010 3 (0·4) 310 (7·5) 0·04 (0·01, 0·14)
Treatment Status, n (%)     
Untreated 35 (4·1) 995 (24·1) Reference*  
Treated 818 (95·9) 3132 (75·9) 6·09 (4·34, 8·55)
Splenectomy Status, n (%)     
Spleen Intact 438 (51·3) 3407 (82·6) Reference*  
Splenectomized 415 (48·7) 720 (17·4) 3·21 (2·81, 3·67)
  1. * "Reference" indicates group used for odds ratios comparison.