This study presents findings on the economic feasibility of a new method to estimate mortality in crisis-affected and resource-poor settings, based on field evaluations in four different sites.
There was significant variance in the time-inputs among the study sites, reflecting their different characteristics. The informant method in Mae La camp in Thailand and the Tanzania camps required only 168 person-hours and 444 person-hours respectively. This was because little travel and data collection time were required due to the low number of deaths recorded and high population density of these camp settings. They also did not require population estimation to be conducted. The study in Tanzania required greater time inputs than Mae La camp principally because two camps were included. By contrast, the study in Chiradzulu District recorded 93 deaths in 96 villages covering an area of approximately 875 km2, and required population estimation, which accounted for almost half of total person-hours (most of which was attributable to villagers hired to count structures). The Kabul site also entailed high person-time inputs, partly due to the requirement to hire additional data collection staff to ensure same-sex interviews and FGDs; population estimation in Kabul, on the other hand, accounted for a small proportion of total person-time (7% of total person hours).
Comparisons between the informant method and conventional retrospective surveys suggest that the informant method could offer considerable economic benefits over retrospective surveys. The informant method required less time than retrospective surveys with a 6 month recall period in three of the four study sites. It also showed considerable monetary savings, with staff cost estimates in all four study sites lower for the informant method than for a survey. In future studies, where accurate population data (for all ages and for under 5 years) are not available, population estimation would be required, stratifying the estimate by age group, as we did in this study for the Kabul and Chiradzulu District study sites. However, even where population estimation is required, the results from our study suggest that the informant method would require less time and monetary inputs than for a survey. Importantly, the recall period for the informant method was 1 month which would be of much greater operational use for relief agencies than a survey with a 6 month recall period, particularly in acute emergencies in which humanitarian agencies need recent mortality data. When the results of the informant method were compared against a retrospective survey with the recall period of 1 month, the time and costs benefits of the informant method increased substantially. However, a drawback of the informant method is that it only measures mortality, whereas retrospective surveys can include other outcomes, such as child nutrition and micronutrient data and vaccination status at little extra cost 
Data entry is substantially less for the informant method than retrospective surveys. If the entire community is surveyed exhaustively, data analysis is also simpler than for surveys by removing the need for weighting and design effect adjustment inherent in sample surveys, or individual person-time calculation when the recall period is long and the cohort very dynamic. The method could therefore be used by programme staff with limited research skills.
Generally, we believe that the informant method would be most feasible in camps and concentrated populations. In post-emergency camps or other communities where population size is being monitored, feasibility results from Mae La and the Tanzania camps represent what might be routinely expected. In chaotic situations where no population estimates are available, time and costs of the population size estimation required for the informant method would be expected to increase.
A major benefit of the informant method was that respondent burden was considerably less than for retrospective mortality surveys, with approximately 90% less time spent by informants on the informant method compared with surveys with a 6 month recall period (rising to over 98% for surveys with a 30 day recall period). Surveys can be burdensome for communities, and reducing respondent time has ethical implications 
. In addition, all key community informants who were found agreed to provide information, and household response was almost 100%.
However, a number of potential ethical issues regarding willingness to participate potentially exist. The referral by key informants who are also community leaders could infringe on the principle of voluntary participation. The informant method exploits hierarchical social structures: deference towards and/or fear of authorities may mean that households might be unable to refuse participation in the study, or decide which information about the decedent they wish to disclose (while introducing bias into estimation, deliberately false answers may be a justifiable way for the household to protect itself against the consequences of sharing certain information with strangers). We did not observe or hear of incidents suggesting any of these dynamics, although we recognise that such delicate issues are difficult to gauge in the short amount of time we spent in each study location. Moreover, the method's reliance on key informants or neighbours to identify households with deaths essentially deprives those households of the choice to disclose the death to investigators, and to some extent to disclose details on the decedent. We also found it difficult to persuade key informants not to be present during the interview (no key-informants were actually present during the interviews but they were present during the initial introductions for around 20% of the households visited), but they should be actively discouraged from being present during the interview to ensure full confidentiality. Follow-up work could be conducted to explore any untoward effects of the referral system that underpins the informant method, and find ways to strengthen the consent and confidentiality arrangements. However, it should also be recognised that similar ethical issues around voluntary participation exist in retrospective surveys which often seek permission for elders and village leaders and such permission can also place pressure on respondents to participate.
The addition of verbal autopsy questionnaires in the Chiradzulu District site took a total additional time of 76.5 hours, 4% of the total person-time input in that site. We believe this suggests that it is feasible to routinely add verbal autopsy questionnaires to the informant method given the reduced time required for conducting the informant method when compared to a retrospective survey. The addition of verbal autopsy questionnaires when measuring mortality rates provides an extremely important way of increasing the accuracy of recording the causes of mortality and so helping to inform appropriate health interventions and responses.
There was a very high willingness of households to respond. If response rates were lower then it would reduce the sensitivity and economic feasibility of the method. However, we do not feel that these high response rates were due to the particular research situations in our study, and the varied settings and populations used for the study provide a good indication that such response rates could be expected elsewhere. We also do not believe there were any aspects of our own research approach that meant response rates were higher in our study than if the informant method was used by other researchers applying sufficient levels of care and the same basic principles and standards required for research in such settings 
The informant method also had only moderate sensitivity and the next steps in achieving better sensitivity would include the use of ethnographic research on how information of death is shared in a community, in a variety of settings, to help refine the informant method procedures and questionnaires for future use. Another round of validating the method in a few more sites, focussing on increasing sensitivity through more effective use of key informants, would also be beneficial. Such sites should include unstable displaced camps with fluctuating populations.
The study has a number of limitations. First, we were unable to test the method in settings of an acute humanitarian crisis where mortality is likely to be highest and where we believe the method would be most useful. This was because we needed a sufficiently stable environment to conduct the validation aspect of this study (from Roberts et al. 
). Second, we were unable to compare the time and costs with actual retrospective mortality surveys as none were conducted in directly comparable locations and time and recall periods. We therefore had to rely on estimations based on assumptions. The time-based approach excluded non-time-based parameters such as materials and supplies (e.g. food, communications, photocopies). However, these non-time-based items are likely to have contributed only a small proportion of costs and so would only have a minor influence on the overall costings. Lastly, the limited sensitivity of the informant method means costs could potentially increase in order to improve the referral information (e.g. use of more key informants) but we also believe that improving sensitivity principally involves more effective selection of key informants and better eliciting of information from them which would not necessarily require additional resources. Improving sensitivity would also mean interviewing more people which would take more time and money. Although it should be recognised that the actual data collection accounted for about 30–50% of total costs, and most of these costs related to driving to sites, making contact with key informants, and obtaining their list of recent deaths, with little incremental cost due to additional interviews. If sensitivity went up from the current 60–70% to 100%, data collection costs would certainly rise, but the overall effect on the total budget of the study would probably be less than 10%. However, our data was not sufficiently detailed to contain the incremental costs required to accurately estimate the additional costs resulting from increased sensitivity.
The validation of the informant method indicated that further work is required to improve the informant method's moderate sensitivity which ranged from 55% to 73% and which was comparable with the well established surveillance systems in Mae La camp and the Tanzania camps, but below the sensitivity level of 80% that we had aimed for when developing the method (see , and Roberts et al. 
for further details). However, the informant method requires fewer resources and incurs less respondent burden, and allows for more time to add additional investigation components such as verbal autopsy questionnaires to obtain more reliable information on the causes of death. We believe that the generally impressive feasibility of the informant method and the near real-time mortality data it provides warrant further work to develop the method, given the paramount importance of mortality measurement and the limitations of current methods to measure mortality.