15/02/2018
Group effects are commonly misinterpreted as individual risk and incorrectly used to make injury prediction for individual athletes. It is important to understand that identifying isolated risk factors or even their interactions with other risk factors, does not enable you to predict which individuals will go on to have an injury.
We often want to simplify results when determining injury risk, but this is not the true picture. To illustrate the point in a different way, we present two ways in which Mike can think about when interpreting the test results:
Reasoning 1:
Decreased eccentric hamstring strength = risk factor for injury
Johnny = Decreased eccentric hamstring strength
therefore
Johnny will get injured
OR
Reasoning 2:
Decreased eccentric hamstring strength = risk factor for injury (at group level)
Johnny = Decreased eccentric hamstring strength (at individual level),
therefore
Although Johnny has decreased eccentric hamstring strength that is associated with an increased risk of injury, he may not have an injury (and someone with normal hamstring strength may have an injury). But since Johnny is part of the group and the risk of the whole group is increased by having decreased eccentric hamstring strength, it is worthwhile improving the hamstring strength of the whole squad as some hamstring injuries will also occur in those with normal hamstring strength. Johnny might still have an injury, but we can improve his odds.
It is not strange that Reasoning 1 is appealing, mainly because it is easy to follow and requires relatively little cognitive effort. The correct approach is, of course, shown in Reasoning 2. The difficulty comes in understanding the statistical process and what the results really mean. Mike now understands that identifying an isolated risk factor in a specific group cannot identify the individual players who will sustain an injury. So when reading results where statistical significance ORs, likelihood ratios and cut-off values are reported, it is also important to look for the distribution of the players in these studies, the effect size or even the absolute difference to understand the clinical value.
Read www.aspetar.com/journal/viewarticle.aspx?id=351 #.WoWmnTOB1o5
Mike is a physiotherapist working at a football club. Before the start of each season, the medical team does their planning for the year. An important part of this planning will be the periodic health evaluation (PHE), which is commonly referred to as the ‘screening exam’. Like many football clu...
