Missing data and valid distributions

Earlier we indicated why it is important to count the number of times no response was obtained for an item.    In analyzing data, a decision has to be made about how to handle the problem of missing data.     We will use the data for the item, "How do you get water," to show how percentages can be calculated when some respondents do not answer an item.

For this item, N equaled 45 and there were 3 questionnaires for which no response had been obtained. The data could be analyzed by finding percentages for all categories including the one for no data.   But knowing the percentage for missing data would not tell us about how water is obtained. A more useful way to get percentages is to remove the frequencies for "no data," get a new N, and then calculate the percentages. The second method is based on a valid frequency distribution that produces a corresponding valid percentage distribution.

Table 17.4. Ways of acquiring water among households in a central Sudanese village: valid percentages

Means used for acquiring water	f	Percent	Valid frequency	Valid percent
Wife and children	23	51.1	23	54.8
Vehicle	13	28.9	13	31
Animals	6	13.3	6	14.3
Missing data	3	6.6
N	45	99.9	42	100.1

In most surveys we expect to find missing data for a few items, but a large percentage of "no responses" for an item indicates a problem with the item. Either it is poorly phrased or some systematic error occurred in the interviewing process. In such a case, the data for that item should not be analyzed.   A large number of "no responses" on a number of items generally means the whole questionnaire was poorly prepared, that interviewing was poorly done, or both.

Presenting univariate data

Frequency distributions provide the first results of data analysis. The next step is to convert distributions to a form that is easy for readers to grasp and that best presents the meaning of your data. Four common ways of presenting univariate data are:

In addition to our description of ways of presenting data graphically, we suggest you look at another description of ways this can be done. A source we recommend is:

Presenting Data Graphically, and Presenting Results.   This site provides brief descriptions of and links to sources of information and guidance on ways of creating effective graphic presentations of data.

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