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The present paper deals with a method of construction of Partial Tetra-allel Crosscs (PTAC) through Doubly Balanced Incomplete Block Designs (DBIBD) and its analysis by explicit expressions of symmetric sums approach. We have also established an inequality for the estimability of individual design components of variance in the Hinkelmann's double crosses model. A simulation study has been carried out to compare the precision of the estimates of genetic components of variana based on the two diIferenf PTAC with same experimental size. A list of DBIBDs will be useful in the construction of PTAC has given in the appendix.

SummaryTING et al. (1990) have proposed a method of constructing approximate confidence intervals on linear Combinations of several variances that are unrestricted in sign. In this article we have proposed modifications of their method. The performances of the proposed modifications are examined using a computer simulation.

An alternative method for determining the approximate lower collrrdence limits for the positive linear combination of two variances based on an approach similar to BULMER (1957) has been proposed. The probability coverage of the proposed alternative limits has been compared with the other existing methods.