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Table 7.6. Item analysis for schooling and house type
House type and occupation, Table 7.7, also showed a substantial relationship. Seventy six percent (76%) of the men with a low level of schooling lived in houses defined as low. A majority, 64% of the men in the high occupational category lived in houses defined as high. Table 7.7. Item analysis for house type and occupation
These results tell us that each item is related to the other items. We can safely assume, therefore, that all three items are independent but related measures of socio-economic status. We can also assume that each item will contribute to the composite score in a consistent manner. If an item is not associated with other items, it should be deleted because it would not add to the composite score. Scoring items After you have selected the best items for an index, the next step is to assign a score or number to each response for each item. In our example, we would need to assign scores for the low and high categories for each of the three items. The usual practice is to assign a 0 to the lowest category, 1 for the next higher category and so on for the remaining categories. Because we had only two categories, the low category for each item was assigned a score of 0 and the high category a score of 1. The composite score for socio-economic status, therefore, could vary from 0 for respondents in the low categories for all three items to 3 for those in the high categories for all three items. Scores of 1 and 2 would occur for any mixture of low and high categories. The resulting composite scores then would be used in subsequent analyses as the measure for social status. Additional considerations Index construction also involves a decision about whether or not to give added importance, called weighting, to certain indicators. Decisions also have to made about missing data and how to test for validity and reliability. These considerations affect development of scales as well as indexes. Weighting indicators An unweighted index is one in which the indicators are of equal importance or, in research terms, are given the same weight. Scores for the indicators are added to get the index score. Baring a strong reason for assigning different weights to indicators, we suggest you use equal weights in any index you construct. A weighted index, on the other hand, is based on giving some indicators greater importance or value relative to others. This is done by multiplying the score of items selected for weighting by some number. The size of the number may be based on knowledge about the importance of one indicator over others or on basis of statistical analysis. Going back to the construction of a socio-economic index, if we had reason to believe that occupation was far more important than years of schooling or house construction, we might decide to give occupation greater weight by multiplying scores for occupation by 2 or perhaps 3. Then the total range of scores for the weighted index would vary from 0 to 4 (if the weight of 2 was used) or 5 (assuming a weight of 3). |
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