Using the age of the research subjects (AGE1) as the time scale, the formula（1）: 
，where α is the age at which the final event occurred. This model assumes that individuals of the same age have the same baseline risk。On the basis of AGE1, while considering the left-truncated age (AGE2) as the time scale, the formula（2）:
，This model assumes that individuals of the same age have the same baseline risk, and at the same time takes into account the left censored information of the follow-up data. Individuals who have entered the study at age a are included in the risk set R(a).Now the question is, how to set the time scale in formula 2 with the stset command in stata，I am stata novice，thanks a lot。
，where α is the age at which the final event occurred. This model assumes that individuals of the same age have the same baseline risk。On the basis of AGE1, while considering the left-truncated age (AGE2) as the time scale, the formula（2）:
，This model assumes that individuals of the same age have the same baseline risk, and at the same time takes into account the left censored information of the follow-up data. Individuals who have entered the study at age a are included in the risk set R(a).Now the question is, how to set the time scale in formula 2 with the stset command in stata，I am stata novice，thanks a lot。
