Data processing is an important stage between data collection and data analysis.
Fortunately, each questionnaire had been allocated an ID number and stored in ID number order. As a result, it was easy to locate the relevant forms and find out what was going on. An extreme example of an erroneous result came about due to lack of adequate procedures for dealing with missing values while entering data. It is sometimes necessary to write a program to extract a subset of data from a large database. In a recent study, it was found that only half of the 100,000 relevant cases were selected for inclusion in the analysis.