Risk difference

<p>The risk difference (RD), excess risk, or attributable risk is the difference between the <a href="/facts/Risk/tbBEDA0V">risk</a> of an outcome in the exposed group and the unexposed group. It is computed as 
  
    
      
        
          I
          
            e
          
        
        −
        
          I
          
            u
          
        
      
    
    {\displaystyle I_{e}-I_{u}}
  
, where 
  
    
      
        
          I
          
            e
          
        
      
    
    {\displaystyle I_{e}}
  
 is the <a href="/facts/Incidence_(epidemiology)/2BB3FlBK"> incidence</a> in the exposed group, and 
  
    
      
        
          I
          
            u
          
        
      
    
    {\displaystyle I_{u}}
  
 is the incidence in the unexposed group. If the risk of an outcome is increased by the exposure, the term absolute risk increase (ARI) is used, and computed as 
  
    
      
        
          I
          
            e
          
        
        −
        
          I
          
            u
          
        
      
    
    {\displaystyle I_{e}-I_{u}}
  
. Equivalently, if the risk of an outcome is decreased by the exposure, the term absolute risk reduction (ARR) is used, and computed as 
  
    
      
        
          I
          
            u
          
        
        −
        
          I
          
            e
          
        
      
    
    {\displaystyle I_{u}-I_{e}}
  
.
</p><p>The inverse of the absolute risk reduction is the <a href="/facts/Number_needed_to_treat/uGJGNpnP">number needed to treat</a>, and the inverse of the absolute risk increase is the <a href="/facts/Number_needed_to_harm/wrTdl1Hc">number needed to harm</a>.
</p>

Risk difference open-in-new

Risk difference