Russell S. Vaught

Comparative allometric growth of the digenetic trematode Metadena globosa (Linton 1910) Manter 1947 (Cryptogonimidae) in three species of Caribbean fishes.

Allometric growth was compared for Metadena globosa from three species of lutjanid fishes from Belize. Significant differences in allometric growth of the trematode involved (1) the oral sucker in all three species of fishes; (2) body width, posttesticular space, pharynx, and testes in Lutjanus analis and Ocyurus chrysurus; (3) forebody, pharynx and acetabulum in L. analis and L. synagris; and (4) forebody and posttesticular space in L. synagris and 0. chrysurus. Differences in the acetabulum of specimens from L. analis and 0. chrysurus and in the testes of those from L. synagris and 0. chrysurus tended to be significant, whereas no significant effect was noted for the hindbody and ovary in any host species.

What if Subjects Can't be Randomly Assigned?

Random assignment to treatment is not always possible in evaluative research. The semi-experimental design discussed here has aspects of both full experimental and quasi-experimental designs. Monte Carlo studies are used to explore and exemplify the strengths and weaknesses of the design. The analysis suggested is found to give unbiased estimates of treatment effects and error mean squares but biased estimates of assignment effects. Some further aspects of the design and its use are discussed.