The same dose of atenolol and pindolol was not used, therefore making it impossible to observe the submaximal efficacy of pindolol.

Single equipotent doses of atenolol and pindolol were used, therefore the same maximal effects were observed with both drugs, masking the submaximal efficacy of pindolol.

The highest possible doses of atenolol and pindolol were used, hence it was not possible to see the submaximal efficacy of pindolol.

Partial agonism can be observed by using multiple doses of each drug, i.e. generating full dose-response curves.