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Table 1 Statistics summarising validity of binary (yes/no) measures of behaviour

From: Statistical considerations in a systematic review of proxy measures of clinical behaviour

  Direct measure  
Proxy measure: YES NO TOTAL
YES a b a + b
NO c d c + d
TOTAL a + c b + d T = a + b + c + d
  1. The sensitivity of the proxy measures is defined as: a/(a+c); its specificity is as: d/(b+d); its positive predictive value as a/(a+b); and its negative predictive value as d/(c+d).