Changes

1. We impute age, race and gender independently.<br>

1. We impute age, race and gender independently.<br>

2. For race, we first try to base imputation on other data (e.g., ethnicity) for the same person.<br>

2. For race, we first try to base imputation on other data (e.g., ethnicity) for the same person.<br>

3. We impute all remaining missing values using only "good" unimputed) data for another person in the same group, or ctrlnum.<br>

3. We impute all remaining missing values using only "good" (unimputed) data for another person in the same group, or ctrlnum.<br>

4. We use each "good" data value only once for imputation.<br>

4. We use each "good" data value only once for imputation.<br>

5. We work backwards over the ctrlnum; then, if necessary, we work forwards.<br>

5. We work backwards over the ctrlnum; then, if necessary, we work forwards.<br>