Equations for Human Factors

Weber's Law

 

Fechner's Law

                                                S=klog(I)

Steven's Power Law
                                                S=cI^b

Error Probability (EP) or Human Error Probability (HEP)

                                            HEP = EP = (# errors/# opportunities)

Reliability

                                    R= (# successes/# opportunities)=1-EP
                                    Of Components in serial       R = P R_i
                                            Of Components in parallel    R = 1-(1-R_i)^c 
                                           (note: this equation assumes that each component in parallel has the same reliability)

Calculation of decibels

                                                                      
 
Calculations of Measures Related to Visual Intensity:
  

 
          Contrast Ratio                    

CR =	Lmax _____________    Lmin

 
 Visual Angle

                                                    a = tan^-1(S/D)