In the study by Pepperberg (parrot learning), the data collected was the parrot's speech. Alternatively, the parrot's actions in response to instructions, such as 'peck yellow square' could have been observed.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

1. [2] Both marks are for the suggestion. 1 mark for identifying an advantage. 2nd mark for detail. An action may be much more obvious / speech could be misheard/misunderstood (=1 mark) So the observers would make fewer errors (=1 mark for detail) this would make observing actions a more valid/reliable measure (both are correct) (=1 mark for detail)
2. [2] Both marks are for the suggestion. 1 mark for identifying a disadvantage. 2nd mark for detail. An action requires an additional instruction / the instruction 'peck' (= 1 mark) the parrot may not understand this instruction (= 1 mark for detail) this would make the parrot appear not to understand the concept (= 1 mark for detail) which would be incorrect / would lower validity (= 1 mark for detail)