Monitoring is a common, yet non-rigorous method of estimating programme effects and is hence prone to errors. Only measuring the changes of outcomes for the population before and after a development programme, there is no way of knowing if the outcome would have remained the same in the absence of the programme. For instance, a monitoring system can observe that the nutrition of a village population improves after everyone in the village has received a crop storage container. However, unless all competing explanations can be eliminated – e.g. changes in agricultural productivity, construction of a new well, changes in income, or the presence of deadly diseases – we cannot be sure that the impact is indeed a result of the intervention.

Monitoring data is nevertheless often used in development work thanks to its ease and low cost for reporting and project evaluations. Monitoring is useful when the focus is on operation, implementation, or service delivery.