ICPSR PROCESSING INFORMATION The data collection was processed according to the standard ICPSR processing procedures. The data were checked for illegal code values, and documentation missing from the NES Study Staff version of the codebook was added to the ICPSR version. Since the NES Study Staff release of the dataset, a new variable, Days Alive (V30), has been added, and the Control Identification Number (V102) has been changed. See the codebook documentation for more detailed explanations of these variables. Data are available in both logical record and card-image format. A data map documenting the column locations for both versions of the data is included at the back of the codebook. ICPSR has also added a Frequencies Addendum to the codebook, with frequencies for all variables except the Case Identification number (V1), Days Alive (V30), the Cluster ID (V102), and all alphabetic variables (V7, V22, V25, V26, and V29).