Limits on compositeness of quarks and leptons from e+e- annihilation

Data of the CELLO experiment on pair production of electrons, muons, taus, and heavy quarks have been investigated in terms of compositeness. CELLO has performed simultaneous measurements of the differential cross sections for cantic and bantib production in e+e- annihilation. Different methods are compared for treating the common normalization errors of the data points when fitting the predicted cross sections. We discuss difficulties in the interpretation of experimental limits on the compositeness scale Λ not mentioned in previous measurements. Λ turns out not to be the appropriate parameter to estimate effects of a possible substructure of quarks and leptons. Limits on Λ from different experiments can neither be compared nor combined with each other. Therefore an analysis of the combined data on fermion pair production from PEP and PETRA has been performed