
            
            Mid-parent / offspring regression as an estimation of  heritability (h2)
          
          
        
         
          The red
            dots show the correspondence between the phenotype
          values of the offspring (Y-axis)
          and the mid-parent
          (the average of the two parents) (X-axis). The red line is the
          calculated regression line,
          which corresponds to the heritability
          (h2).
          Perfect heritability would be indicated by a line with slope
            = 1.0 (dashed blue
          line). Here, the points are somewhat more scattered,
          and the slope and heritability are calculated as h2 =
            0.5. 
          
              Notice that this analysis is a regression,
          rather than a correlation, because by the hypothesis
          the midparent value predicts the offspring
          value. Absent such a hypothesis, the analysis is
          mathematically a correlation, because the midparent value is
          not controlled, that is, chosen for pre-determined values of
          1.1, 1.2, 1.3, and so on.
         
      
        
    
    Figure ©2002 by Griffiths et al.; all text material ©2025 by
          Steven M. Carr