The four Manuals in this cluster explain methods for estimating population size, mortality and fertility with the emphasis on situations when data from censuses and civil registration are insufficient or unreliable. In addition, Manual II is devoted entirely to the methods of appraising the quality of basis data for demographic estimates. Manual X is the backbone of this cluster. It contains a comprehensive compilation of techniques suited for the analysis of incomplete or defective demographic data. Since demographic estimates constitute the basis of any demographic analysis, all other Manuals on this website are related to this cluster. Particularly strong ties connect this cluster to the clusters Demographic Models and Population Projections.