I am a non-native speaker trying to find the right expression for my sentence. There is a study that reports a 55% decline in the number of trades, however, I cannot examine the data or the study itself. I would like to express that I only quote the number without any kind of double-check by myself. To express this, 'apparently' and 'allegedly' come into my mind. My sentence with these two options:
Apparently: "In fact, the number of trades apparently declined by about 55 % after its introduction (citation)."
Allegedly: "In fact, the number of trades allegedly declined by about 55 % after its introduction (citation)."
At first, I was going for 'allegedly', but then I felt that allegedly somehow transports that I do not believe that this information is true or that I have at least serious doubts. I do not doubt this fact but I also do not have any evidence that it is true.
To be more precise, what I want to say is that there is a study that reports a 55% decline, but I do not have much information of the study and only quote the number. I would like to express that I did not examine the study but simply reproduce what others have stated.
Further clarification as to why I wish to add something beyond the citation: Usually, a citation alone should be enough. However, in this case, the citation refers to a report that cites this number as the result of a study by the authors without specifying data or details of the study (something like "We compared A with B and found a 55% decline"). The citation alone might suggest that I have examined this study, which is not the case.