Composite quality index of silk cocoons—application of discriminant analysis

Journal of the Academy of Business and Economics, March, 2004 by Vishuprasad Nagadevara

ABSTRACT

The quality of silk cocoons is determined by a number of characteristics. Each of these characteristics measures a different aspect of the quality. In the absence of a single measure for the overall quality, the price of the cocoons is based on one or two characteristics, which are deemed to be most important by the buyer or the seller. It is shown that there is very little correlation between these characteristics. A methodology is developed to create a composite quality index (CQI), which encompasses all the important characteristics. The cocoons are graded into three categories, Low, Medium and High quality based on the CQI. Discriminant analysis is used to map the individual characteristics directly on to the three grades of cocoons. It is shown that the discriminant functions are significant and that the functions are able to classify the cocoons into the grades with a high degree of accuracy. Once the cocoons are graded using the discriminant functions, the buyers and the sellers could negotiate the price with complete information about the overall quality of the cocoons.

1. INTRODUCTION

Sericulture occupies a very important position in the Indian economy. Its structure comprising of mulberry cultivation, silkworm rearing, silk reeling and fabric weaving spreads across the agriculture sector, industrial sector as well as cottage industries and export units. Thus it plays a pivotal role in economic development of the country by generating employment, incomes as well as foreign exchange. By the very nature of its structure, sericulture faces the problems associated with both agriculture and industries, especially cottage industries. It is one particular segment of sericulture namely the reeling segment, which faces the brunt of the problems associated with both the sectors, namely the agriculture and industry.

In spite of India being a large producer of raw silk, cocoons are transacted without testing and the cocoon price is purely based on the subjective assessment of quality made by the buyer at the time of purchase. There is neither a system for scientific assessment of the quality of cocoons prior to transaction nor a systematic approach for fixing the price based on their quality and market conditions (Vasumathi, 2000).

It has been established that cocoon quality contributes to the tune of about 80 per cent of the raw silk quality (Shimazaki, 1964). As a result, some form or the other of quality index as a measure of cocoon quality exists in countries more advanced in sericulture especially Japan and China (Somashekar, 1999 and Nakajima, 1999). These countries have realized the importance of cocoon quality in the price fixation and made the cocoon testing mandatory prior to marketing. In addition, the cocoon price in these countries is fixed on the basis of the cocoon quality as well as the price of raw silk, which is fixed on an annual basis.

At the same time, the national standards used by other sericultural countries cannot be adopted as such in the Indian context (Vasumathi, 2000). Therefore, there is a need for developing an objective method of assessing the quality of cocoons based on the parameters so that an organizational mechanism to bring its implementation to cocoon transactions can be set up.

Cocoon quality is governed by several parameters, each of them being associated with a certain level of importance (Anon, 1996). Some of the important quality parameters usually considered are: Shell Ratio percentage, Defective Cocoon Percentage, Average Filament Length, Average Non Broken Filament Length, Denier, and Reelability percentage. Of these, Shell Ratio percentage and Defective Cocoon percentage have been identified as the most significant ones (Sonwalkar, 1982, 1993) especially because these are relatively easy to determine requiring minimum facilities, infrastructure and time.

It has been established that each of the quality parameters has its own relative significance on the reeling efficiency and raw silk quality. The procedures for assessment of a few of these parameters are quite involved, while it is relatively easy for a few others. A few tests are non destructive (as in the case of Defective Cocoon percentage), while a few are destructive (as in the case of Shell Ratio percentage). Thus, each of the parameters is associated with a certain extent of ease or difficulty in assessment.

The important characteristics that define the quality of cocoons are described below:

Single cocoon weight (SCW): This is simply the average weight of a cocoon. This is usually calculated by selecting 25 cocoons at random, then taking the total weight and then calculating the average of a single cocoon weight. This is measured in grams or centigrams.

ii. Shell weight (SW): This is the average of the single shell weight. The shell is that portion of the cocoon after removing the pupae. This is calculated by taking the same 25 cocoons that are used for calculation the single cocoon weight. The pupae are removed from these 25 cocoons and then the average weight of the shells is calculated. The shell yields the raw silk and hence the higher is the shell weight, the higher is the yield of the raw silk. This is also measured in grams or centigrams.