Last updated on .From the section Football

Jonjo Shelvey (left) has been capped four times by England

Newcastle's £12m purchase of Swansea midfielder Jonjo Shelvey was the best-value signing of the January transfer window, according to a study.

Analysis from the CIES Football Observatory external-link says the 23-year-old England international is worth £23.5m.

Its data suggests Chinese club Guangzhou Evergrande paid £18.43m too much when they spent £31m on Atletico Madrid striker Jackson Martinez.

Bournemouth are said to have overspent on £7m Norwich striker Lewis Grabban.

According to the CIES research team, which analyses transfers in Europe's big five leagues, that was more than £6m too much.

Best-value signings of winter transfer window (CIES Football Observatory) Name From To Fee Underpaid by Jonjo Shelvey Swansea Newcastle £12m £11.5m Augusto Fernandez Celta Vigo Atletico Madrid £5m (reported) £2.48m Mario Suarez Fiorentina Watford £4m (reported) £2.24m

The study also suggested Newcastle overpaid by £5.4m when they spent £12m signing England winger Andros Townsend from Tottenham.

That move went through on 27 January, the same day Chinese club Jiangsu Suning signed Brazil midfielder Ramires.

The 28-year-old moved in a deal believed to be worth about £25m, which the CIES study claims is £8.36m more than his value.

Worst-value signings of winter transfer window (CIES Football Observatory) Name From To Fee Overpaid by Jackson Martinez Atletico Madrid Guangzhou £31m £18.43m Ramires Chelsea Jiangsu Suning £25m (reported) £8.36m Lewis Grabban Norwich City Bournemouth £7m £6m

How does it work?

The CIES Football Observatory team of academics estimates transfer values based on 1,500 fee-paying deals involving the big five European leagues since June 2009.

It takes into account the "inflationary trend" of transfer fees and calculate a player's worth based on their statistics in six key areas - age, position, contract, international status, experience and performance.

Footballers with the highest transfer values in the study generally play in competitive teams, are active full internationals, play in attacking positions, have long-term contracts and are under 27 years of age.