Momentum is one of the most prized commodities in football. Barcelona have had it all season, Manchester United had it and then mislaid it, and Liverpool supposedly had it before being blown away by Chelsea on Wednesday night. Now Chelsea and Arsenal, having struggled to find top form for most of the season, have found the momentum that could lead to major silverware. The good news for teams at both ends of the Premier League table is that it is not too late to gather some momentum. At this stage of last season, Fulham had fewer Premier League points than current bottom club West Brom, having won only four games out of 31. Roy Hodgson then somehow conjured four wins from Fulham's last seven games, which enabled them to escape relegation on goal difference. The difficulty for football punters is how to measure momentum: is it a short-term commodity, or something built over the longer term? Here is one measure that might be useful and informative: an index that compares the points gained in the first four months of the season (the opening 15 games for most Premier League teams) with points in the past four months (covering the next 16 games for most teams). A positive index indicates a team on the up; a negative index points to a team on the slide. The top team on this index is Blackburn, who took just 13 points from their first 15 games but have taken 21 from their last 16 (all of that improvement has come under Sam Allardyce, who has secured those 21 points from 14 games in charge). Tottenham are next-best, followed by West Ham, Everton, Manchester City and Arsenal. The index puts numbers to the general perception that those six teams have been improving in recent months, and it also throws into sharp relief the declining form of several struggling clubs. Middlesbrough come out worst: having opened with 19 points from 15 games, they have added just eight points from their last 16 games. Early high-flyers Hull have fared little better than Middlesbrough in recent months and Portsmouth have been in poor form too. Relegation was the outcome for two of the four teams that were regressing and had fewer than 35 points at this stage of last season, which points to continuing difficulty for Middlesbrough, Newcastle, Portsmouth and Hull. Two of that quartet could be sucked down with West Brom, who are positive on the index but look doomed. This weekend could be pivotal in the relegation battle, with six of the bottom eight facing each other today. Portsmouth host West Brom, Middlesbrough are at home to Hull and Newcastle travel to Stoke for their first realistic chance of victory under Alan Shearer. On the following two weekends, at least four of those eight teams will be in opposition, and that could be the springboard for one of those teams to perform a Fulham-style escape - last season Fulham's final seven games included clashes with the three teams that were relegated. Portsmouth are the relegation-threatened team showing the strongest signs of building some momentum, having improved under Paul Hart with nine points from six games. They have a game in hand and four of their last eight games are against teams in the bottom eight, including three of the four teams below them in the table. One point of interest is that three of the bottom four teams on the index - Middlesbrough, Hull and Bolton - are among the Premier League clubs not to have changed manager this season. The top three on the index, by contrast, have gained momentum since changing manager. The bottom two in the league table have stood by their managers despite poor results - Middlesbrough with Gareth Southgate and West Brom with Tony Mowbray - and relegation for those two clubs would be a blow to those who argue that loyalty to managers, rather than the sack, is the best policy. While the teams at the bottom will be fighting for their lives, it could pay to be more wary of the mid-table teams who are clear of the relegation zone but whose European hopes are fading. Four of the five teams in places 8th-12th at this stage of last season were among the worst performers on the run-in, and this season Wigan, Fulham, Manchester City, Tottenham and Bolton could fade in the closing weeks of the season. Even though Tottenham have been one of the form teams in recent weeks, they could be worth opposing at home to West Ham tonight. The Hammers have been in good form too - no team outside the top six has taken more points in the past four months - and they look overpriced to take something from White Hart Lane. Gunner get better Arsenal are the form team in the English Premiership as they are unbeaten in (games): 17 Treble chance Manchester City have lost five times this season at home. A trio of those have come after Uefa Cup ties: 3 SHORTLIST Milan, Fiorentina, West Ham, QPR, Bristol City, Sheffield Wednesday, Watford, Walsall, Lille, Monaco. BEST BETS $200 West Ham (handicap HAD, Sat), QPR (handicap HAD, Sat), Monaco (handicap HAD, Sun). FORM FACT Newcastle have drawn 11 of their 31 games, the highest number in the Premier League. Alan Shearer needs to find a way to turn some of those draws into wins - and fast.