ScotRail has missed a key performance target amid "challenging" autumn and winter conditions on the railways.
In the 12 months to January 6, 90.4% of trains met a target of arriving within at least five minutes of their scheduled time, against a target of 91.7%.
The figure was 83.4% for the four-week period ending January 6.
Transport Minister Humza Yousaf has previously said he expected the target to be met by the end of 2016-17 after the introduction of a performance improvement plan.
ScotRail highlighted incidents that had impacted on performance, including signalling and points failures, and said railway industry expert Nick Donovan had been drafted in to carry out an independent review of performance.
ScotRail Alliance managing director Alex Hynes said: "Despite the challenges of recent months, ScotRail remains the best performing large operator in the UK.
"For nine out of ten of our trains to have met the target time over the past year is a strong foundation on which to build.
"But because we want to deliver even more for our customers, and because we rightly expect the highest standards, we will come forward with a performance improvement plan.
"Our customers deserve a better and more consistent service from us, and we are determined to deliver that."
Mr Yousaf said he expected the recent downward trend to be addressed "immediately".
He said: "I completely understand the frustration of any passenger who has had their journey impacted by poor performance.
"ScotRail has faced a number of challenges not least the impact of seasonal weather, which affects most UK operators, however this on its own can't and won't be used as an excuse.
"Given that 54% of performance issues are infrastructure-related there is a clear need for the greater devolution and better governance arrangements for Network Rail in Scotland which we have called for so many times.
"Closing this accountability gap and improving efficiency is a necessity as we move towards a system of grant-based funding from 2019 onwards.
"It should be acknowledged the existing performance improvement plan had been working well but the dip in performance since Autumn must and will be addressed."
Labour's connectivity spokesman Colin Smyth said the figures strengthened the case for public ownership of ScotRail.
He said: "Passengers in this country already pay some of the highest fares in western Europe for a service of delays, overcrowded trains and stops being skipped to leave people stranded. It's no wonder that customer satisfaction with ScotRail is not improving.
"Humza Yousaf said ScotRail would be hitting these targets by the end of 2017 - the minister should explain what has gone wrong.
"Scottish Labour would take ScotRail back into public ownership and deliver a people's railway that puts passengers first."
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