I am trying to understand top coding for the variable TRANTIME. It appears to be top coded at 158 minutes. I found on the IPUMS USA page (https://usa.ipums.org/usa/volii/top_bottom_codes.shtml) that:
“Age, travel time to work, and all base dollar amounts are top-coded using the state mean of all cases greater than or equal to the top-code state minimum value.”
I can’t seem to find a definition for “the top-code state minimum value”, which would help me understand what cases are used to calculate the mean.
Any ideas?
Thanks!
Top-coding occurs in the ACS when a response to a particular question exceeds a certain threshold. For example, participants who report wage income above a certain threshold (e.g., $500,000) have their wage income top-coded by replacing the reported value with a different value. Top-codes for each variable are dynamic and vary by state and year. The maximum value that you see in the data (158 minutes) only refers to the top-code for a single state in a single year. Top-codes are typically applied to encompass the top 0.5% of values in each state for each year. The values that are selected for top-coding are replaced with the mean value of the cases selected for top-coding. If there were only two respondents who reported their wage income above the $500,000 threshold in the example above (e.g., $600,000 and $700,00), both of their wage incomes would be reported instead as $650,000.
The “top-code state minimum value” refers to the threshold value used for top-coding since it is the minimum value for which responses received a top-code. It can be found in the original PUMS .csv file at the bottom of the page that you link to. The column titled JWMNTPCT reports the threshold value for TRANTIME while T_JWMN reports the value that top-coded responses to TRANTIME were assigned.