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ties = A tie occurs when two data points are equivalent to one <br />another. Y -tied groups are the number of VOC or inor- <br />ganic concentration groups which are the same over time. <br />The computer program corrects the tau and Z values for <br />tied groups. Unless there are no tied groups for a particu- <br />lar parameter, the Z values corrected for ties are used to <br />evaluate trends in VOCs and inorganic constituents. <br />p = Probability that an observed pattern of increases or <br />decreases over time is not a trend. <br />To reject H, the probability corresponding to the Z value <br />(corrected ?or ties) must be less than the specified <br />a value. The smaller the probability value, the greater the <br />probability is that a trend is occurring, and the greater <br />likelihood that time (the independent variable) can be <br />used to predict the VOC or inorganic concentration (the <br />dependent variable). <br />In this example, p = 0.0406. This value is small and is <br /><0.05, the a value. Therefore, we can reject HO of no <br />trend and determine that a downward trend is occurring. <br />pjb\b02\bO20104j A-4 Rev. 0 September 25, 1991 <br />