The Tobit model from the previous section assumes a normal distribution that is censored at zero. An observation of zero is considered to be left-censored. In the Fit Parametric Survival platform, left-censored observations are specified using two response columns. In this example, you create a new column that indicates observations for which left censoring has occurred. For left-censored observations, the new column contains a missing value. Otherwise, it contains the observed value of durable. The new column is then used as the left side of interval-censored observations, and the existing column durable is used as the right side of the intervals.
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Select Cols > New Columns.
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Select Comparison > a == b, type 0, and press Enter.
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Figure 13.14 Column Formula for durable0
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Click OK.
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Click OK.
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Select Analyze > Reliability and Survival > Fit Parametric Survival.
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Click Run.
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Figure 13.15 Tobit Model Results