5.1 METHODS FOR INDICATOR ESTIMATION
An estimate is an approximate value calculated on the basis of the incomplete evidence or available data.
Almost all calculations of health indicators are based on estimates irrespective of whether the data was collected by direct measurements or by indirect measurement techniques; in both cases there is a margin of error. Where a direct measurement is involved, inaccuracies can stem from random errors that are inherent in the sampling processes or from systematic errors due to the procedures used to select the population, collect the data, and its subsequent analysis. In the case of estimates based on indirect measurements techniques that use mathematical or statistical models, inaccuracy can also occur because of inherent errors in the methodology owing to the assumptions and limitations of the model. Assumptions in such models are difficult to assess. This is particularly so in small populations where valid and replicable data and information are limited and, especially in the absence of sufficiently long and reliable times series.
This section uses the term estimate to refer to estimation by indirect methods based on techniques that employ mathematical and statistical models or other demographic techniques to adjust or correct direct data. Thus, estimates of indicators by indirect methods are in contrast to the direct calculation of indicators, which are based exclusively on data and information from primary or secondary sources of information.