A sample based on 90 percent of actual bus fleet data for all transit approximates the universe. Many of the modal statistics that BTS and DOT use as a matter of routine are based on less than 90 percent of the universe. In this estimate, sampling errors are not a serious problem. Nonsampling errors are primarily a result of noncoverage errors. Not all data errors are related to poor sampling techniques.
Some errors are measurement or coding errors.
Data may not be gathered from some groups. These errors are discussed in this section. Nonentry Error or Missing Data - The NTD program is required by statute. Without an annual NTD submission, FTA grant funds are cut off. The response rate is near 100 percent.