The increasing needs for more disaggregated data motivates National Statistical Offices (NSOs) to develop efficient methods for producing official statistics without compromising on quality. In Indonesia, regional autonomy requires that Sustainable Development Goals (SDGs) indicators are available up to the district level. However, several surveys such as the Indonesian Demographic and Health Survey produce estimates up to the provincial level only. This generates gaps in support for district level policies. Small area estimation (SAE) techniques are often considered as alternatives for overcoming this issue. SAE enables more reliable estimation of the small areas by utilizing auxiliary information from other sources. However, the standard SAE approach has limitations in estimating non-sampled areas. This paper introduces an approach to estimating the non-sampled area random effect by utilizing cluster information. This model is demonstrated via the estimation of contraception prevalence rates at district levels in North Sumatera province. The results showed that small area estimates considering cluster information (SAE-cluster) produce more precise estimates than the direct method. The SAE-cluster approach revises the direct estimates upward or downward. This approach has important implications for improving the quality of disaggregated SDGs indicators without increasing cost.
The paper was prepared under the kind mentorship of Professor James J. Cochran, Associate Dean for Research, Prof. of Statistics and Operations Research, University of Alabama.
The increasing needs of evidence-based policy making underpins the increasing demand for official statistics . National Statistical Offices (NSOs) play a prominent role in providing information for various aspects such as business and policy decision, public discussion and scientific research . NSOs are demanded to produce more disaggregated, timely, and diversified statistics without compromising on quality. With limited resources, NSOs need to find an efficient way to achieving this purpose .
Indonesia has a decentralized governance system called ‘regional autonomy’. This system provides authority to local (provincial and district, with district being the lower level) governments to manage their regions for their own development. As a consequence, official statistics are needed to monitor regional developments up to the district level. BPS (Statistics Indonesia), the Indonesian NSO, is responsible for providing official statistics up to the district level through its regular surveys.
The regional autonomy system implies that Sustainable Development Goals (SDGs) targets are not merely adopted in the national development plan, but also integrated into local development plans. According to the regional autonomy system, each district in Indonesia is an important policy maker for the nation’s development.
Indonesia has a strong commitment to achieve the SDGs, including in the field of family planning. Target 3.7 of the SDGs declares that universal access to sexual and reproductive health-care services, including for family planning, information, and education, should be achieved by 2030. This target also mandates that reproductive health should be integrated into national strategies and programmes by that year as well. In the National Medium Term Development Plan (RPJMN) of Indonesia, the modern method contraception prevalence rate (mCPR) is targeted at 63.41% in 2024, while unmet needs for family planning are expected to decline to 7.4% by 2024.
Indicators for family planning targets are normally derived from the Indonesia Demographic and Health Survey (IDHS). The IDHS is conducted every five years with collaboration of the Indonesian National Population and Family Planning Board (BKKBN), Statistics Indonesia (BPS), and the Ministry of Health, which collects information about fertility, family planning, maternal and child health, etc. The most recent update of the IDHS in 2017 covers 1,970 census block samples in urban and rural areas and 47,963 successfully interviewed households. In the interviewed households, 49,627 eligible women and 10,009 eligible men were interviewed completely.
The 2017 IDHS used a two-stage stratified survey designed to produce estimates at national and provincial levels. Therefore, there are gaps for district level policies. One of alternative ways to fill these gaps is by increasing the sample size in the survey. However, this approach would be very costly and resource-intensive. Other strategies are needed to disaggregate the indicator statistics without increasing costs and the respondent’s burden.
The Small Area Estimates (SAE) method has been considered as a more cost-effective strategy . Some studies also point out that SAE enables more reliable estimation of small areas by utilizing auxiliary information from other sources. This method can artificially increase the effective sample size and thus increase the precision of estimation .
Statistical techniques for SAE are diverse. Model-based is a frequently preferred method, where the specific area statistics are estimated from the regression between response variable from survey and auxiliary information from administrative data or census . On the other hand, the Empirical Best Linear Unbiased Predictor (EBLUP) method is an indirect way to predict small area parameters. However, standard EBLUP uses a synthetic model that ignores area random effects for non-sampled areas . As a result, the resulting estimates are distorted into a single line of the synthetic model and may result in considerable bias .
In this paper, similarities among particular areas were used to estimate area random effects for non-sampled areas. This approach was used to estimate the contraception prevalence rate (CPR) at district level in the North Sumatera province. From 33 districts in North Sumatera, there are 6 districts that were not sampled in 2017 IDHS. The idea of incorporating cluster information into the standard EBLUP has been proposed by Anisa et al. . This approach was modified in several ways: 1) partitioning around medoids algorithm was used to generate clusters. This algorithm will be explained later; 2) a logit transformation was used to ensure that CPR estimates fall between 0 and 1; and 3) the area level model was used rather than unit level model.
Data was acquired for the CPR in North Sumatera province from the 2017 IDHS and auxiliary variables from the Family Planning Coordinating Board of North Sumatera. To eliminate the scale effects, these auxiliary variables were transformed into standardized values. These auxiliary variables were only available at the district level. Table 1 lists the auxiliary variables used in this study.
|No.||Variable||Description||Unit of measure|
|1||Z||Number of active acceptors||Person|
|2||Z||Number of family planning clinics||Unit of clinics|
|3||Z||Number of family planning institution||Unit of institution|
|4||Z||Number of pre-prosperous and 1 prosperous family||Unit of family|
These auxiliary variables were used in identifying clusters and estimating the CPR using the SAE model. For the clustering process, the Human Development Index (HDI) was also considered so districts could be grouped based on their development levels.
This paper employs partitioning around medoids (PAM) algorithm to generate clusters. A medoid is simply the object from a cluster with the minimum average distance to all other objects in the cluster. Using this procedure, objects are randomly chosen as initial medoids. Then the distance between all objects and the medoids is calculated, and each objects is assigned to the cluster of its nearest medoid. For each created cluster, the distance between all member objects is computed, and the objects with minimum sum of distances is chosen as the new medoid. This continues iteratively until no objects change clusters, or the maximum number of allowed iterations has been exceeded .
The advantage of PAM is that it is less sensitive to outliers. As in -means clustering, the number of clusters () in PAM (or sometimes called -medoids) is predetermined. The number of clusters () is determined using the elbow method. The principle of elbow method is to choose a number of clusters so that adding another cluster does not give much decrease in total within sum of squares .
Cluster information is further incorporated into the standard SAE model. Cluster information is utilized to estimate area random effects for non-sampled areas, which can be written as:
where is the area random effect of sampled areas in th cluster, is the number of sampled areas in th cluster, and is the estimates of area random effect for non-sampled areas in th cluster.
This paper used the CPR as an indicator to be estimated and must take a value in the interval [0, 1]. A logit transformation was used to ensure that the CPR estimates fall between 0 and 1.
In particular, is approximately normally distributed with mean and variance . Therefore, the variance estimator is as follow:
where is the sample proportion of married women using contraception (CPR) in th area and is the sample size in th area.
Finally, the standard area level model is modified as follows:
• Model for population:
• Prediction model for sampled area:
• Prediction model for non-sampled area:
where is the sample proportion of married women using contraception (CPR) in th area, is the vector of standardized auxiliary variables in th area, is the vector of parameters, are dummies for cluster, is the area random effect, is the error term, denotes a non-sampled area, and is the estimate of area random effect for non-sampled area.
If is the compound vector of parameters and is the compound vector of predictors (auxiliary variables and dummy variables) in th area, then the estimates of and could be derived as :
where is the area-specific sampling variance and is the area random effect variance. Since is unknown, then it is estimated using Restricted Maximum Likelihood (REML) method.
This paper employs R software to derive estimates of , , and . Confidence interval of
Figure 1 depicts the resulting total within the sum of squares as a function of the number of clusters. Using the elbow method, the number of clusters was selected for which adding another cluster does not substantially decrease the total within the sum of squares. The figure shows that the total within the sum of squares decreases substantially when up to five clusters are used. Adding clusters at this point does not reduce the total within sum of square substantially. Six clusters would reduce the total within sum of squares by 16.47 units, while five clusters would reduce the total within sum of squares by 27.45 units. Thus, it was chosen to identify five clusters. Figure 2 visualizes the generated clusters derived using the PAM algorithm. This figure clearly shows that the five clusters are generally well-separated.
|Cluster||Number of cluster members||Districts|
|1||5||Nias, Nias Selatan, Pakpak Bharat, Nias Utara, Nias Barat|
|2||14||Mandailing Natal, Tapanuli Selatan, Tapanuli Tengah, Tapanuli Utara, Labuhan Batu, Dairi, Karo, Humbang Hasundutan, Batu Bara, Padang Lawas Utara, Padang Lawas, Labuhanbatu Selatan, Labuhanbatu Utara, Gunungsitoli|
|3||8||Toba Samosir, Samosir, Sibolga, Tanjungbalai, Pematangsiantar, Tebing Tinggi, Binjai, Padangsidimpuan|
|4||3||Asahan, Simalungun, Serdang Bedagai|
|5||3||Deli Serdang, Langkat, Medan|
Note: non-sampled area.
Table 2 presents the members of each cluster. Cluster 1 includes five districts; this includes one non-sampled district (Nias Utara). This cluster has the lowest development and family planning status. Cluster 2 consists of fourteen districts, including three non-sampled districts: Mandailing Natal, Padang Lawas Utara, and Labuhanbatu Selatan. This cluster has a moderate development and a moderate family planning status. Cluster 3 consists of eight districts, including two non-sampled districts: Samosir and Tanjungbalai. This cluster has a lower family planning status. Cluster 4 and cluster 5 each have three members. There is no non-sampled district in either cluster 4 or cluster 5. The districts in cluster 4 (Asahan, Simalungun, and Serdang Bedagai) and cluster 5 (Deli Serdang, Langkat, and Medan) generally have a higher family planning status.
The results from above clusters were further utilized to estimate area random effects for non-sampled areas and construct the area level model that incorporates cluster information as follows:
• Prediction model for sampled area:
• Prediction model for non-sampled area:
A comparison between direct estimates and small area estimates that incorporate cluster information (SAE-cluster) is presented in a 95% confidence interval form in Fig. 3. The point in the middle of interval represents the corresponding point estimate of CPR, and the upper and lower limits of each interval respectively represent the upper and lower bounds of the corresponding 95% confidence interval for CPR (the SAE-cluster model revises the direct estimates). Confidence intervals of the SAE-cluster were generally shorter than the direct estimates. This suggests that the SAE-cluster model produces more precise estimates than the direct method.
A spatial distribution of the CPR estimates using direct estimation and SAE-cluster estimation are provided in Fig. 4. Missing values in direct estimates occur because some areas were not sampled in the 2017 IDHS. This issue is well handled by the SAE-cluster approach using information from sampled areas within the same cluster. The SAE-cluster approach revises the spatial distribution of CPR estimates in North Sumatera province and changes the relative position of several districts.
Another approaches have been proposed to handle the issue of non-sampled area. One of the frequently preferred method is the Spatial EBLUP (see [16, 17, 18, 19, 20]). This method utilizes spatial dependencies among regions to derive estimates for sampled areas as well as non-sampled areas. However, this approach is not applicable in this study since the Moran’s I test indicated that the area random effects are not spatially correlated (Fig. 5).
Incorporation of cluster information into small area estimation offers two advantages. First, it enables the sampled small areas to be estimated reliably. It enhances the precision of the estimates substantially. Hence, it addresses the issue of small samples at the district level. Second, it serves as a procedure for producing superior estimates of area random effects for non-sampled areas that support the development and assessment of comprehensive policy-making. This approach can help NSOs to meet the needs of more disaggregated statistics without increasing costs since this approach uses existing available data sources.
The authors are deeply indebted to Professor James J. Cochran for his warm mentoring, valuable advice and thoughtful guidance during the re-drafting process of this paper. Deep thanks are also expressed to the United Nations Economic and Social Commission for Asia and the Pacific (UNESCAP) for the opportunity to develop this paper and to contribute to global statistical community. Finally, sincere gratitude is expressed to BPS-Statistics Indonesia in supporting the study and providing data for it.
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