4.4 Test of Potential Factors Causing Discrepancy
4.4.1 Using Sampling Weights
Distribution of Population across Provinces
Before constructing weights to match the regional distribution of the IFLS and the Sakernas to the Census, I compare the provincial distribution and urban/rural distribution by province among the IFLS, the Sakernas, and the Census/Inter-Census. Since Sakernas only covered adult members (older than or equal to 15), I compare the provincial distribution of adults between the IFLS and the Sakernas. I also compare the provincial distribution among different sub-samples within the IFLS. These subsamples are all respondents, adults and adults with full work information (who have answered the adult information module or are covered in 1993 by the household economy module). From Figure 4.4 we can see that the IFLS provincial distribution differs significantly from the Sakernas provincial distribution in all of the four survey years of the IFLS. In general the Sakernas provincial distribution is closer to the census and inter-census. Both the IFLS and the Sakernas under-sampled the largest provinces, namely, West Java, Central Java and East Java, and over-sampled Jakarta, Yogyakarta, Bali, West Nusa Tenggara and South Kalimantan. The provincial distribution within the Sakernas is stable over the four years. The provincial distribution within the IFLS is stable from 1993 to 2000, but in 2007, the percentage in North Sumatra, West Sumatra, South Sumatra and South Sulawesi increased significantly compared with the previous IFLS survey years.
I also checked whether the provincial distribution is similar across different sub-samples within the IFLS (everyone, adults and adults with full work information). It turns out this distribution is not significantly different across different sub-samples of the IFLS.
Distribution across Urban/Rural Status within Provinces
The earliest census/inter-census from which I can obtain information on urban/rural population shares by province is the 2000 census. Therefore, the Sakernas and the IFLS distributions in 1993, 1997 and 2000 are compared with the 2000 census. As shown in Figure 4.5, the urban/rural distribution is very different across provinces according to the 2000 census and the 2005 Supas (inter-census). The provinces on the Java-Bali island are more urban compared with provinces on the other islands. Also, the IFLS urban/rural shares differ significantly from the Sakernas.
We can see from Figure 4.5 that in 1993, 1997 and 2000, the Sakernas tends to oversample urban areas in provinces outside Java-Bali island. Especially it oversampled Lampung, South Kalimantan and South Sulawesi. At the same time, it under samples urban areas in provinces on Java-Bali for the same three years. In 2007, the Sakernas urban/rural distribution by province is more similar to the 2005 Supas compared with earlier Sakernas years, even though the differences are still significant.
The 1993 IFLS urban/rural distribution is more similar to the 2000 census than the 1993 Sakernas for all provinces except North Sumatra, West Sumatra, South Sumatra and West Nusa Tenggara. For Lampung, West Java, Central Java and East Java, the 1993 IFLS distribution is very similar to the 2000 census. For Bali and West Nusa Tenggara, the 1993 IFLS has a lower urban percentage than the 2000 census. For the rest of the provinces, the 1993 IFLS has a higher urban share than the 2000 census. This same pattern persisted for the IFLS until 2000. In 2007, the IFLS has a greater urban share for all provinces compared with the 2005 Supas. The 2007 Sakernas distribution seems to be closer to the 2005 Supas distribution than the 2007 IFLS distribution.
I also checked the urban/rural distribution by province for different sub-samples within the IFLS, and I found that the urban/rural distribution by province is not very different across different sub-samples within the IFLS.
Employment Measures after Using Sampling Weights
Figure 4.6: Percent of Adults (older than 15) who Work without and with Sampling Weights
Figure 4.7: Percent of Adults (older than 15) who Do Wage Work without and with Sampling Weights
Figure 4.8: Percent of Adults (older than 15) who Do Non-Wage Work without and with Sampling Weights
As explained in Section 4.2, the 1993 IFLS stratified on province and urban/rural status. Also, as shown above, the provincial distributions in the IFLS and the Sakernas differ significantly from each other and also from the Census distribution. In a country with massive regional diversity, samples with very different provincial distributions may not be directly comparable. Therefore, for each year (1993, 1997, 2000, 2007) of the IFLS and each year (1993, 1997, 2000, 2007) of the Sakernas, I compute sampling weights that match the provincial distribution by urban/rural status to the 2000 census. Then I can find out whether the difference in the provincial distribution is one of the causes of the gaps between the IFLS and the Sakernas by recalculating the employment measures using the sampling weights. In the IFLS, I match the distributions of everyone (all ages) included in the survey to the census. In the Sakernas, I match the distribution of adults (equal and over 15) to the census. The weights are shown in Appendix K. Figure 4.6 to Figure 4.8 compare the trends without using weights with the trends using weights. We can see that using provincial weights does not narrow the gaps between the IFLS and the Sakernas in percent working. In fact, the trends with and without the provincial weights are very similar.