Along with studies reporting high concussion rates, increased concussion awareness among athletes, parents, coaches and health care providers, and new state concussion safety laws has come rapid growth in the use of computerized neuropsychological testing to evaluate and manage sports concussions, particularly at the college and high school levels.
By establishing an athlete's baseline or "normal" score on tests of cognitive functions that are often affected by concussion, such as memory, processing speed, reaction time, and attention, and on measures of physical/emotional/cognitive symptoms, re-testing after a suspected concussion can help determine if and when an athlete's brain has recovered. If the youth feels symptom free, and post-concussion testing is the same or better than baseline (pre-concussion) testing, recovery is imminent.
At least that's the way it's supposed to work.
In practice, however, I have unfortunately found in treating athletes after concussion that too many arrive at my office with invalid baseline test results from their schools: baseline scores that can't be used, because they don't provide an accurate snapshot of a child or teen's pre-concussion or normal cognitive functioning, and so can't be used to measure the degree of post-concussion cognitive impairment and recovery. Two research papers - one on which I am lead author,  the other on which I am a co-author,  confirm my anecdotal experience as a clinician, suggesting that between 6 and 12% of baseline tests may be invalid. An earlier study of college athletes reported a rate of up to 25% invalid baselines. 
Factors leading to invalid baseline test results
Baseline test results can be invalid for a variety of reasons.  The most obvious - recently highlighted by the media in professional sports - occurs when athletes intentionally perform poorly on their pre-season tests in order to establish low baselines that increase their chances of "passing" a post-concussion test and being medically cleared to return to play before their brains have actually healed. Given the increased risk of a second concussion or, worse, a catastrophic brain injury from second impact syndrome, a youth athlete willing to fake a baseline test in order to return to a contact or collision sport too soon, to borrow a phrase, needs a wake-up call!
Most of the time, however, there tend to be other reasons for "invalids" among the youth athlete population.
Some of these reasons include:
- Environmental factors. Distractions during testing, especially when testing is performed in groups, in noisy settings, or with others in the room who are behaviorally acting out. Further complicating matters is the fact that post-concussion testing is not generally performed in a group setting but, rather, alone in a quiet, distraction-free room, Because the whole point is to compare post-concussion test results with baseline results, it's important to try to limit the chance of distraction or interruption as much as possible during baseline testing.
- Reading difficulties or failure to pay attention to the instructions.
- Attentional or learning difficulties that lead to inconsistent results [note: neuropsychological disorders, such as ADD/ADHD, are viewed as a so-called "modifying factor" in managing concussions by the most recent international consensus statement on concussion in sport. 
- Lack of effort, negative attitude, or not taking the test seriously. In some cases, the athlete may just not "feel like" taking the test, or may not be "in the mood." This can often be attributed to a lack of education about the importance of the test. If the athlete doesn't understand why the testing is being performed, or how the testing works, or why she needs to try her best (in order to ensure an accurate, valid score), she may be inclined to answer haphazardly or randomly just to get the thing over with. This is why I recommend explaining the procedure and the importance of baseline testing to athletes before they even reach the testing site.
- "Sandbagging." There is widespread speculation among concussion specialists that some athletes might be inclined to underperform on a baseline test - on purpose - so that if they were made to take a post-concussion test, they would perform comparatively better and therefore be allowed to return to play sooner. Trying to prevent intentional sandbagging is incredibly difficult for test administrators (not to mention parents). This is one reason that the online version of the ImPACT neurocognitive test is programmed to automatically flag test protocols that seem suspicious.  A 2012 study  showed that, while it is possible for athletes to "sandbag" their baseline neuropsychological testing without reaching threshold on "red flags" or validity indicators, with the study finding that only 11% were able to do so successfully, it is difficult for athletes to perform significantly more poorly on their ImPACT baseline than they are capable. A 2013 study  confirmed that intentionallly underperforming on baseline testing using ImPACT is extremely difficult to achieve without detection. Using built-in validity indicators in ImPACT, 70% of those told to malinger without guidance, and 65% of coached malingerers were detected. Using the forced-choice validity measure with the Word Memory portion of ImPACT, 95% of naїve malingers and 100% of coached malingers were detected. The results of the two studies suggest that inspection of baseline test results will identify 70% to 90% of athletes attempting to sandbag their baselines.
- Fatigue, illness, or testing after an athletic practice or game.
- Right-left confusion when using a computer mouse or keyboard.
- Faulty equipment, such as a computer mouse that sticks or doesn't function properly.
- Color blindness (especially if the test items require color discrimination).
Unfortunately, many baseline testing programs are conducted en masse in schools with limited athletic or school staff to oversee and review test results. As a result, baselines tend to be automatically stored in databases, but may not be looked at again until a concussion occurs. Some computerized neuropsychological tests now in use automatically identify or "flag" test results that may be invalid.
Advice to parents
So what should parents, schools and testing centers do to ensure that their child's baseline test is valid?
My advice is to make sure that the people in charge of obtaining a baseline for your child:
- Routinely review all baseline test results immediately afterwards and re-test when there is possible invalidity (a recent survey of 399 athletic trainers at various high schools, colleges and universities found that 95 percent of respondents reported using ImPACT for baseline testing, but only 54.8% actually examined the validity of those results; 
- Know the test indicators that signal possible invalidity;
- Thoroughly explain the test to athletes before the test is taken and make sure he or she understands the instructions, and instructing student-athletes to raise their hands if they have questions or problems;
- Provide a quiet, controlled environment for testing, with seating that is comfortably spaced so that athletes are not seated so close to each other or across from one another, soundproofing or white-noise machines to drown out extraneous sounds or interruptions;
- Having one or two trained test administrators (e.g. a credentialed ImPACT provider) present at all times;
- Identifying and removing an athlete who is overly talkative or disruptive, and testing him or her later individually;
- Testing when fatigued is not an issue (ideally, the testing should not be performed at the end of a long day, immediately following exercise, practice, or a game, or if the athlete has not slept the night before [8,9] (completely sleep-deprived athletes reporting for baseline testing should be rescheduled for testing after a normal night's sleep).
- Understand and control for the factors that may affect test results.
The bottom line is, as a recent study emphasized, to remember that "comparisons made between baseline tests and follow-up testing [after concussion] are only valid if baseline testing truly represents normal functioning and extraneous factors influencing the scores are taken into account."
1. Moser RS, Schatz P, Neidzwski K, Ott S.D. Does Group vs. Individual Administration Affect Baseline Neurocognitive Test Performance? Am J Sports Med (in press)
2. Schatz P, Moser RS, Solomon GS, Ott SD, Karpf R. Incidence of invalid computerized baseline neurocognitive test results in high school and college students. J. Ath Tr 2012;47(3):289-286.
3. Broglio SP, Ferrara MS, Macciochi SN, Baumgartner T A, Elliott R. Test-retest reliability of computerized concussion assessment programs. J Ath Tr 2007;42(4):509-541.
4. Consensus Statement on Concussion in Sport: the 4th InternationalConference on Concussion in Sport held in Zurich, November 2012. Br J Sports Med 2012;47:250-258.
5. Erdal K. Neuropsychological Testing for Sports-related Concussion: How Athletes Can Sandbag Their Baseline Testing Without Detection. Arch Clin Psych 2012;27(5):473-479.
6. Covassin T, Elbin R, Stiller-Ostrowski J. Current sport-related concussion teaching and clinical practices of sports medicine professionals. J Athl Train 2009; 44(4):400-404.
7. Schatz P, Glatts C. "Sandbagging" Baseline Test Performance on ImPACT, Without Detection, Is More Difficult than It Appears. Arch Clin Neuropsychol (published online ahead of print February 11, 2013)
8. McClure DJ, Zuckerman SL, Kutscher SJ, Gregory A, Solomon GS. "Baseline Neurocognitive Test Results in Non-concussed Athletes: Does Sleep Matter?" Presentation paper, AOSSM (June 13, 2013)
9. Mihalik JP, Lengas E, Register-Mihalik J, Oyama S, Begalle R, Guskiewicz KM. The Effects of Sleep Quality and Sleep Quantity on Concussion Baseline Assessment. Clin J Sport Med 2013;23(5):343-348.
Most recently revised September 13, 2014