Personal view: Christmas might be the most wonderful time of the year, but for retailers it's also the most critical. Nowhere does this argument apply more than in the grocery sector where all eyes will be on Tesco to see whether the company has managed to turn around its recent poor performance. The likelihood is that it will post a reasonable set of numbers, largely thanks to weak comparatives and a very strong promotional push. We already know that Waitrose has had a stellar Christmas and trading at Marks & Spencer's food division is also likely to be solid. Asda, along with the deep discounters, have driven home the right messages of value combined with indulgence and treats, so will also be within the winner's circle. That leaves Morrisons and Sainsbury's, with the former the favourite to come in bottom of the grocery pile. Notably, one of the factors acting against Morrisons has been its lack of an online presence; especially problematic this Christmas when internet shopping has truly come of age. While reports that online accounted for the majority of sales this Christmas are wildly exaggerated, it is true that the growth differential between online and physical has been significant, the former has probably grown by around 15% while the latter has been virtually flat. Next is an excellent case in point for the difference that a strong online presence made this Christmas: without internet sales, its performance would have been virtually flat rather than in solid positive territory. John Lewis has also been a major investor in online and its click and collect service, which provided consumers with the convenience of a true multichannel proposition, is one of the reasons it will is likely to be crowned the high street winner this Christmas. Regardless of channels, this Christmas has seen some clear trends in terms of consumer and buying behaviour. The food discounters and value players, like Aldi and Poundland, have seen sales boom as people have tried to make limited budgets stretch further. It has not all been about austerity, however. The premium end of the market in both food and non-food has done well as many shoppers now equate quality with value for money. Selfridges, Fortnum & Mason, Ocado, House of Fraser and many of the niche clothing players will present numbers that are solid to strong. Of course, this trading up has come at the expense of volume: if anything, this has been a Christmas of buying better, but fewer products. Premium has also been the order of the day in electricals where relatively expensive branded product, like Apple's iPad, Samsung's phones or Amazon's Kindle Fire, have been flying off the shelves. Thanks to this, and to the failure of Comet, trading at Dixons, the only remaining significant electricals specialist, will have been robust. Others too, including John Lewis and Amazon have been beneficiaries of the gadgets boom. Players stuck in the middle are likely to post a very mixed set of numbers. Marks & Spencer's performance in general merchandise will be given much scrutiny and results are predicted to be fairly soft. Given that last year's performance was relatively strong and that sales of fashion in December were fairly weak, the jury is currently out on Debenhams performance. WHSmith and Boots will also be ones to watch: the latter with its deals and offer and strong performance in gifting categories is likely to be OK, the former has probably ceded share in things like cards, wrap, books and entertainment to rivals. Given that there is great variability in what and how retailers report, seasoned commentators and casual observers alike should give adequate consideration to the context in which numbers are presented. Looking at the trading period, the comparatives from last year, the variance between total and like-for-like sales and any margin guidance will all help to provide a rounded picture of performance. The bottom line is that when all of the numbers are in while some retailers will have experienced their most wonderful time of the year, others will have suffered from rather bleak trading. Sadly, such polarisation isn't just for Christmas, it's here to stay. Neil Saunders is managing director at retail analyst Conlumino