CHAPTER 4: METHOD EVALUATION
4.5 Internal Coherence
82 across quintile five was the highest for the dichotomous PCA index for four of the six countries.
Table 4.7 is a summarised description of the differences in the mean SES scores between the quintiles and the frequency histograms for the distribution of SES across the six countries for all four methods. The distribution of SES scores was uneven for all four methods across all six countries, except for Egypt where the differences in mean SES between the quintiles were more equal than for any of the other countries and the SES frequency histograms showed a less-skewed distribution. For each country, the SES distribution was less skewed and the differences in mean SES scores between the quintiles were more equal for the simple sum method than for the others.
Table 4.7: SES score distribution of the total sample of households for all methods across the six countries
Source: Author‟s calculations
83 the groups of households. Using three classification groups - poor, middle and rich - Filmer and Pritchett (2001) found large differences across the groups for almost all the index variables. For example, 96 per cent of the „poor‟ used biomass as a cooking fuel, whereas only 22 per cent of the „rich‟ did so.
By way of example, the results of the analysis of the Malian household data undertaken in this study, using the dichotomous PCA method of index construction, are discussed in detail below. A summary of the internal coherence of the four methods across all six countries is then presented. Of the households in each of the first three quintiles, greater than 40 per cent obtained drinking water from an unprotected well, only the fifth quintile was different to the other quintiles in that 30 per cent of households had water piped into the dwelling and 36 per cent used a public tap or standpipe as a source of drinking water. Regarding the variables related to the type of toilet facility, quintile one was characterized by no facility/bush/field (76 per cent), more than 60 per cent of the households in each of the second to fourth quintiles used a traditional pit latrine and greater than 50 per cent of households in quintile five used a ventilated improved pit latrine. The variables relating to the type of toilet facility did not show internal coherence across all five quintiles; rather they were able to distinguish between three groups, quintile one, quintiles two to four and quintile five. For the variables relating to the type of floor material, the first four quintiles were similar and characterized by a floor material of earth or sand, only the fifth quintile differed noticeably with more than 70 per cent of households having a dwelling with a cement floor. For the first four quintiles, the main material used as cooking fuel was wood – more than 78 per cent of households in each quintile. Only for the fifth quintile did the frequency of wood use drop substantially: 44 per cent of households in the fifth quintile used charcoal as a cooking fuel and only 51 per cent used wood.
Considering the durable asset variables, houses in the first quintile were characterized by a lack of ownership of assets: 33 per cent of households owned a radio, 34 per cent owned a bicycle and 2 per cent owned a motorcycle or scooter - no other assets were owned by households in the first quintile. Across quintiles two to four, asset ownership was similar with more than 70 per cent of households owning a radio and more than 48 per cent owning a bicycle for each quintile. In contrast, all of the asset variables were owned by at least some of the households in the fifth quintile, with 88 per cent possessing a radio and 59 per cent owning a motorcycle or scooter. Ownership of a television increased between the fourth and
84 fifth quintiles: only 28 per cent of households in the fourth quintile owned a television, whereas 75.5 per cent of households in the fifth quintile did so. No households in quintiles one to four owned a refrigerator, while 21 per cent of households in the fifth quintile did so.
In terms of internal coherence for the Malian dataset using the dichotomous PCA method of SES index construction, there were relatively large differences in ownership of, or access to, the various variables between the first and the fifth quintiles, but there was not always much distinction between adjacent quintiles. Similarly, as shown in Table 4.5, there was a difference in mean SES score of 0.96 between quintile one and two, but a difference in mean SES score of 8.88 between quintile four and five. These results suggested that the index of SES constructed here using Malian households was able to distinguish between the „poor‟
and the relatively „richer‟, but the index was not able to separate out the households in- between quintiles one and five with as much clarity. Forcing the Malian households into five equally sized groups may not have been the best means of classifying the households based on the estimated SES score, since a larger proportion of the sample had relatively low SES scores. The five groups did not display the desired internal coherence and applying arbitrary cut-off points, such as the quintile split, did not reflect the clustered nature of the Malian data.
Table 4.8 presents the observations made with regards to internal coherence for the four methods across the six countries. The observations were made by comparing the frequency of household access to or ownership of each of the variables across the five quintiles. As suggested by Filmer and Pritchett (2001), internal coherence can only be concluded if there is a difference in asset ownership across the quintiles. Internal coherence could not be concluded for all, or even the majority, of variables for any of the methods across all the countries. In almost all instances, quintile five was distinct from the other quintiles, but there was often similarity in the frequency of access to, or ownership of, the variables between quintiles one to four.
The simple sum method appeared to be the best at separating households into five quintiles as at least three of the variables included in the simple sum method showed internal coherence across the five quintiles for all the countries. From these results, it is suggested that grouping the households into five equally populated categories is not an appropriate means of household classification when using an index of SES, regardless of the method of index construction. This conclusion is strengthened by the SES distribution results, discussed
85 previously, which indicated that SES was not evenly distributed across households for any of the countries, except perhaps for Egypt.
Table 4.8: Internal coherence (a difference in frequency of access to or ownership of the variables between quintiles) for each of the methods across the six countries
Table 4.8: continued
Source: Author‟s calculations