Jonjo Shelvey
Jonjo Shelvey joined Newcastle United in JanuaryGetty Images

Newcastle United's capture of Jonjo Shelvey was the best-value transfer of the January window, according to a new study. The Magpies acquired the England international from Swansea City for a fee of £12m ($17.3m), but the CIES Football Observatory has claimed the 23-year-old midfielder is, in fact, worth as much as £23.5m.

Based on the CIES data, Chinese club Guangzhou Evergrande were guilty of the least-savvy bit of business, paying £18.43 million too much when they splashed £31 million on Atletico Madrid striker Jackson Martinez.

Similarly, Bournemouth are said to have overspent on £7m Norwich striker Lewis Grabban, while Newcastle apparently overpaid by £5.4m when they forked out £12m for England international Andros Townsend.

Elsewhere, Chinese club Jiangsu Suning signed Chelsea midfielder Ramires for a fee believed to be worth about £25m. However, the study claims the Chinese Super League side overpaid for the player by more than £8.3m.

The CIES study is based on the work by a team of academics who looked at 1,500 fee-paying deals involving the big five European leagues since June 2009. The analysis considers "inflationary trend" of transfer fees.

The report calculated a player's worth based on their statistics in six different areas – age, position, contract, international status, experience and performance.

Premier League clubs spent £175m overall in the January transfer window, with Newcastle, Norwich City and Watford accounting for around 40% of the total. As well as signing Shelvey and Townsend in big-money deals, Newcastle also bought Henri Saivet from Bordeaux and loaned striker Seydou Doumbia from Roma in a bid to stave off relegation.