Demographic and Health Surveys Methodology - Measure DHS

The figure on the previous page illustrates the nature of the hierarchical structure of a typical DHS surveyin which two separate questionnaires (household and woman) are used to collect information.The example shows that, while a single questionnaire is always completed for each household in the DHSsample, the number of Women’s Questionnaires that will be completed depends on the number of eligiblewomen listed in the Household Questionnaire. In other words, for each Household Questionnaire theremay be zero or several women questionnaires.The hierarchical data file produced in ISSA has a two-level structure reflecting the relationship betweenthe questionnaires; the Household Questionnaire is at Level 1 and the Women’s Questionnaire(s) atLevel 2. Within each ISSA level, there can be one or more different types of records. For example,records in the household level in the typical DHS file can be single (e.g., household characteristics) ormultiple (e.g., household members listing). Thus, using the same file, it is possible to work with differentunits of analysis (households, household members, women and children). This makes the analysis ofvariables across different units easy.The hierarchical structure defined by ISSA has several advantages and disadvantages. Among theadvantages, the following can be highlighted:• All the data is stored in just one ASCII file. Virtually all statistical packages can read ASCII files.• Since all the data is stored in the same file, it is easy to maintain the integrity of the data in terms ofdata structure related to levels and records.• The data file mirrors the paper questionnaire. Each section in the questionnaire can be defined as arecord in the data file and only the information that is needed is present in the file.The major disadvantage is that this structure can be easily handled only by ISSA, CSPro, or by acustomized program written in low-level computer languages such as C, C++, FORTRAN, or Basic toname a few.Flat FilesIn a flat file there is one record for each case. All variables in each case are placed one after the other onthe same record. The multiple or repeating records of the file are placed one after the other on the record,with the maximum number of occurrences of each section being represented in the data file. Each variablein a repeating section is placed immediately after the preceding variable of the same occurrence, such thatall variables for occurrence 1 precede all variables for occurrence 2 of a section. The length of the recordin the flat data file is fixed.Rectangular FilesIn a rectangular file each case in the data file contains a fixed number of records. Each record in thehierarchical file will have a representation in the rectangular file. For multiple or repeating sections thereis a record for each occurrence of the section, with the maximum number of occurrences of each repeatingsection included in the data file. Essentially, the rectangular file looks the same as the hierarchical file butwith blank records padded whenever the record does not exist in the hierarchical file or to complete themaximum number of records in repeating records.Guide to DHS Statistics 6 September 2003