The current transfer window has been something of a 'dry January'. 

Premier League clubs have spent under £100 million combined since the New Year and it's easy to see why. 

The mid-season market is often characterised by panic buys and late, scrambled short-term fixes. 

Of course, some clubs are better than others at spotting value for money. 

Liverpool have a fantastic track record when it comes to their January acquisitions, having signed Luis Suarez, Philippe Coutinho and Virgil van Dijk in the winter window - though they were also guilty of splashing out on Andy Carroll from Newcastle. 

Since Michael Edwards arrived as technical director, their business has only got better.

That's been evidenced by ESPN's study of the best and worst transfers in the Premier League since 2014/15. 

Deals have been rated on a number of factors, including:

- Minutes played 

- Price paid compared to actual valuation 

- Whether the player's rating has improved since the deal 

- How the player's market value has changed since the deal 

- Actual transfer fee 

Let's start with the best: 

5. Ricardo Pereira, Porto to Leicester, 2018 -- Fee: £22m (Current value: £24m)

The Leicester full-back is perhaps one of the Foxes' unsung heroes with eight assists and five goals in his last season-and-a-half, despite having come from the Primeira Liga as something of an unknown quantity. 

4. Mohamed Salah, Roma to Liverpool, 2017 -- Fee: £34m (Current value: £100m)

How on earth did Liverpool pull this one off? Granted, Salah had not been a hit in English football previously but he was on fire at Roma in his last season in Serie A and had also impressed with Fiorentina. The Egyptian would be worth at least 3x that market value now - but the truth is, he's priceless.

3. Georginio Wijnaldum, Newcastle to Liverpool, 2016 -- Fee: £25m (Current value: £56m)

The Dutchman had done enough to impress for Newcastle despite their season ending in relegation from the Premier League. Wijnaldum cost just £25m but has since become an integral part of the European champions' midfield. 

2. Dele Alli, MK Dons to Spurs, 2015 -- Fee: £5m (Current value: £53m)

Dele Alli has been a trailblazer for players coming up from the lower leagues. MK Dons recouped what seemed like a huge £5m for the teenager but he has since become an England regular and a Champions League finalist. When his brother's not playing, anyway. 

1. Andy Robertson, Hull City to Liverpool, 2017 -- Fee paid: £8m (Current value, per 21st club: €82m)

Hull had just been relegated when Liverpool took a gamble on their young left-back, probably seeing him as more of a back-up option than anything else. Robertson has since been transformed into the best left-back in Europe and has notched up 24 Premier League assists. That form has seen the Scotsman's value increased by 14x. 

As for the worst? 

There are five players whose value has plummeted since they moved clubs and none of them come as a surprise. 

5. Kelechi Iheanacho, Manchester City to Leicester, 2017 -- Fee: £24m (Current value: £7.6m)

Iheanacho has actually started to prove himself as a competent back-up to Jamie Vardy of late. As a whole, though, he's scored 17 goals in his last 75 games. It's not a horrendous tally, but for a striker who as a youngster was neck-and-neck with Marcus Rashford, the way his career has transpired is a little disappointing. 

4. Oumar Niasse, Lokomotiv Moscow to Everton, 2016 -- Fee: £15m (Current value: £2.2m)

Niasse is now worth just a fraction of the £15m Everton forked out to bring him in from Lokomotiv Moscow - which just about sums up the Toffees' transfers since Farhad Moshiri took over. 

3. Ben Gibson, Middlesbrough to Burnley, 2018 -- Fee: £15m (Current value: £1.1m)

Gibson was once courted by Manchester City and Spurs when he was at Middlesbrough. Sadly for the English defender, he has never really fulfilled the potential that convinced Burnley to pay a club record £15m for him. 

2. Eric Bailly, Villarreal to Manchester United, 2016 -- Fee: £30m (Current value: £8.3m)

If minutes on the pitch have been a deciding factor, it's clear why Bailly's value has slumped. The Ivorian has been so unlucky with injuries, but it has to be acknowledged that he's made errors when he has played too. Bailly was once the centre-back Jose Mourinho believed would fix United's defence. It didn't work out that way. 

1. Michy Batshuayi, Marseille to Chelsea, 2016 -- Fee: £33.2m (Current value: £8.4m)

Batshuayi's goals kept Marseille up in 2016 and simultaneously sparked a clamour for his signature between Chelsea and Tottenham. The north Londoners must be breathing a sigh of relief that he opted for Stamford Bridge, where he's been sent on loan three times. 

It's easy to berate Liverpool for spending big on the likes of Alisson Becker and Van Dijk, but their transfer strategy is seriously smart. 

Chelsea, United and Everton have a lot to learn from them.