Stratum

Effective

Positive

Negative

Strate 1

173

41 (23.7%)

132 (76.5%)

Strate 2

174

46 (26.4%)

128 (73.6%)

Strate 3

173

52 (30.1%)

121 (69.9%)

Total

520

139 (26.7%)

381 (73.3%)