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When measuring the difference between performance, prices, quantities or indeed any other value of something, it is common to measure the most recent value against the value measured exactly a year earlier. Year on year (yoy) is often used to avoid confusion with a change in value in the calendar year to date (ytd), or indeed the financial year to date (ytd). For example a company who reports, in June perhaps, that its share price has risen 5 per cent year on year, might have seen its share price jump by 10 per cent in the year to date, if most of the price movement had been in more recent months.
At the end of 2012 analysts were observing that Chinese refined copper net imports had risen 73 per cent year on year (yoy). In another example of its use in January 2013, UK high street pub chain JD Wetherspoon warned that operating margins for the half year to January 27 would drop 1.1 per cent year on year to 8.2 per cent.