Since I last wrote about advanced screeners for UK value investors, the kind you have to pay for, Stockopedia has emerged as my favourite.

Empirical Finance Data looked promising but abruptly stopped delivering. With its machine written reports that bear some comparison to broker analysis, Capital Cube is so stacked with features it’s barely recognisable as a screener but it’s not priced for typical private investors.

I use Sharescope, which is a Windows program rather than a website, exclusively for tracking the value of portfolios. For screening, it lacks important fundamental measures and much of the data only goes back five years. Company REFS, a revolutionary product when it was invented, is beefier in some respects, but has similar limitations.

Sharelockholmes includes ten years of data and more statistics. It’s also very cheap. I use it to calculate the state of the market.

For data, though, Stockopedia shines. The company lets me publish some of its data, you can find its F_Scores in the Annual Results Report, but before you write this review off you might consider why I went to Stockopedia for the data.

One of my regular features in Money Observer magazine tracks the Nifty Thrifty, a portfolio picked using a mechanical investing strategy based on Joel Greenblatt’s Magic Formula and the F_Score.

Once you have picked a mechanical investing strategy, the quality of the data used to generate buy and sell recommendations is really all that matters, but algorithms like the Magic Formula and the F_Score are not trivial to calculate. They require very specific figures plucked from company accounts and many of the services aimed at private investors simply don’t have all of them. Instead they approximate the ratios, or leave them out entirely.

Stockopedia has the data, supplied by Reuters, it’s open about the robust way it calculates the financial statistics and, crucially, they’re up to date. By up to date, I don’t just mean that for most companies the site updates a day or two after they publish results but also, uniquely among the sites I use, Stockopedia calculates trailing twelve month figures rather than using the last reported annual results. To do this it must piece together figures from quarterly and half-year income and cash flow statements.

Screening with annual results is less satisfactory because companies report at different times of the year, so the results the screeners compare might not actually be comparable.

Stockopedia also scores with the simplicity and sophistication of its screening interface, which allows investors to fork (i.e. clone) screens, rank and compare ratios with each other, and market averages.

Beyond screening, it’s a fast, attractive website that provides excellent page at a glance company summaries. Of course, the richness of the pages are possible because of the data beneath, which allows it not only to compute, but explain how it’s computed, other novel statistics like the Altman Z-Score, a predictor of bankruptcy, and the Beneish M-Score, which identifies companies that may be manipulating earnings.

I should mention the founders’ commitment to publicising value investing and stock screening, a preoccupation of Ed Croft who writes frequently on the site, which also syndicates the content of respected UK Bloggers. Stockopedia tracks the performance of numerous mechanical investing strategies including the Nifty Thrifty, and publishes their recommendations. It should become a fascinating resource as the months turn into years.

Stockopedia has limitations, currently most of the data only goes back six years, it lacks information about major shareholdings and the director deals are tucked away on a separate page hidden among other news. But Stockopedia also has an encouraging record of plugging limitations so if ''20 a month, or ''180 a year can be absorbed by your trading costs, it may be worth trying out.