Below is my own analysis based on Inderes recommendations and Yahoo Finance stock data. Only companies listed in Helsinki are included. Stock data has been retrieved from the day following the recommendation date.
In the first review, the investment period extends until the next recommendation. On average, Buy recommendations have yielded the best returns, and Sell recommendations the worst. The returns for Accumulate and Reduce recommendations are also logical.
It’s important to note that returns include a lot of variation. For Buy recommendations, the return can be expected to be between -10.1% and 13.9% in 68% of recommendations. Relative to the average return, a Buy recommendation provides the best return-risk ratio among the recommendations.
A new recommendation has been given approximately every 43 days, regardless of the previous recommendation. By examining only the direction of the return, it is observed that the direction matches the recommendation with approximately 53% probability.

When defining returns according to 50, 100, 200, and 300 calendar days, more variation is visible in the returns. The Accumulate recommendation has offered the best return over 200 and 300-day periods.

There is some variation in the standard deviations of returns across different time periods, but no extremely large differences.

The best return-risk ratio of 0.32 is achieved with an Accumulate recommendation and a 300-day period. The return-risk ratio is better than always investing according to the recommendation. Of course, the recommendation can practically remain the same, in which case no changes to the investment would be needed. Trading costs have not been considered in the returns, which is worth keeping in mind. Over 200 and 300-day periods, the return-risk ratios are between 0.25-0.32, so longer-term investments seem more reasonable. Trading costs would further change the situation to favor a longer investment period.
Edit: corrected a minor error in the code and slightly adjusted the calculation of returns