Gross Motor Function Measure (GMFM)

What is the GMFM?

The Gross Motor Function Measure (GMFM) is a clinical tool designed to evaluate change in gross motor function in children with cerebral palsy. There are two versions of the GMFM - the original 88-item measure (GMFM-88) and the more recent 66-item GMFM (GMFM-66). Items on the GMFM-88 span the spectrum from activities in lying and rolling up to walking, running and jumping skills. The GMFM-66 is comprised of a subset of the 88 items identified (through Rasch analysis) as contributing to the measure of gross motor function in children with cerebral palsy. The GMFM-66 provides detailed information on the level of difficulty of each item thereby providing much more information to assist with realistic goal setting.

GMFM scores of a sample of over 650 Ontario children with cerebral palsy with varying GMFCS levels have been used to create five Motor Growth Curves. These curves describe the patterns of motor development of this sample of children and are similar to the growth charts that are used to follow the height and weight of children as they grow.

Who is the GMFM appropriate for?

While the original measure was designed and validated for children with cerebral palsy, there is evidence that the GMFM-88 version of the measure is also valid for use with children with Down Syndrome. The updated GMFM-66 version is ONLY valid for use with children with cerebral palsy.

As the GMFM-88 samples motor skills that are typical of normal developmental milestones, it may be useful for children other than those with whom it has been validated; however reliability and validity should be established prior to using it with other groups of children.

The original validation sample included children 5 months to 16 years of age. The GMFM (either version) would be appropriate for children whose motor skills were at or below those of a 5-year-old child without any motor disability.

How is the GMFM administered?

The GMFM should be administered in an environment that is comfortable for the child and is large enough to hold the necessary equipment and allow the child to move freely (e.g. one item requires the child to run 4.5 m (15 feet) and return). The floor should be a smooth, firm surface. Because the GMFM was designed to measure change over time it is important to keep the environment and assessment conditions as consistent as possible for each assessment.

How is the GMFM scored?

There is a 4-point scoring system for each item on the GMFM. Specific descriptors for scoring items are detailed in the administration and scoring guidelines. The item scoring is the same for the GMFM-88 and GMFM-66. The GMFM-88 item scores can be summed to calculate raw and percent scores for each of the five GMFM dimensions, selected goal areas and a total GMFM-88 score. The GMFM-66 requires a user-friendly computer programme called the Gross Motor Ability Estimator, or GMAE, to enter individual item scores and convert them to an interval level total score.

How long does the GMFM take to administer?

Administering the GMFM-88 may take approximately 45 to 60 minutes for someone familiar with the measure, depending on the skill of the assessor, the ability level of the child and the child's level of cooperation and understanding. The GMFM-66 should take less time to administer as there are fewer items.

What qualifications are required to administer and score the GMFM?

The GMFM was designed for use by pediatric therapists who are familiar with assessing motor skills in children. Users should familiarize themselves with the GMFM guidelines and score sheet prior to assessing children. It may be helpful to practice on several children with and without motor disabilities prior to using it for clinical assessments. It is recommended that users assess their reliability with the GMFM prior to using it.

What equipment is necessary?

The equipment required is described in detail in the GMFM Manual. Most of what is needed is standard equipment in a physiotherapy gym (e.g. mat, bench, toys). Access to stairs (with at least 5 steps) is also necessary.  

Ordering the GMFM Manual

The Gross Motor Function Measure (GMFM-66 and GMFM-88) Users' Manual 2nd edition(2013) can be ordered through Wiley Blackwell Publishing. Cost information is available from the publisher.

GMFM Score Sheets

GMFM Score Sheets are available with open access for download and printing for personal, non-commercial use.

Please note that the GMFM-66 and its shorter forms (GMFM-66-IS and GMFM-66-B&C) requires a computer program (called the GMAE) to score it. We recently updated the GMAE (GMAE-2) and have made it available on the CanChild website. To download a copy, please click here to be redirected to the appropriate page.

Translations of measures and materials on the CanChild website are performed by individuals who are fluent in both English and their own language. CanChild requires a back translation of the document by a different person than the original translator to ensure accuracy. The customs and culture of various regions may not be reflected accurately unless a validation study has been conducted.

GMFM-66 Tabulated Reference Percentiles

Tabulated reference percentiles are available for use with the GMFM-66 to assess children with cerebral palsy. The percentiles are presented by GMFCS levels, and are suitable for scientific or clinical use in conjunction with the GMFM-66 manual. The percentiles are derived from a longitudinal sample of 1940 GMFM-66 assessments of 650 children with CP, 2 - 12 years of age. This stratified (by age and GMFCS) random sample was collected from among all children with CP who were receiving a variety of developmental therapies and services at publicly funded children's rehabilitation centres in Ontario, Canada, between 1996 and 2001.

The development and appropriate use of these percentiles is described in:

Hanna, S.E., Bartlett, D.J., Rivard, L.M., & Russell, D.J. (2008). Reference curves for the Gross Motor Function Measure: Percentiles for clinical description and tracking over time among children with cerebral palsy. Physical Therapy 88(5) 596 - 607. doi: 10.2522/ptj.20070314

GMFM FAQ's

FAQs relating to the GMFM-88

What is the GMFM-88?

The GMFM-88, or Gross Motor Function Measure 88 (previously known as the GMFM or Gross Motor Function Measure), is the original 88-item measure designed to evaluate change in gross motor function over time or with intervention for children with cerebral palsy. It has also been validated for use with children who have Down syndrome.

Who can use the GMFM-88?

The GMFM-88 was designed for use primarily by physical therapists who are familiar with children with cerebral palsy, and the administration and scoring criteria outlined in the manual.

How can someone learn to use the GMFM-88?

It is important for someone wanting to learn the GMFM-88 to read through the manual with particular emphasis on the administration and scoring guidelines. Practice with several children will help users feel comfortable with the items and administration methods. Comparing GMFM-88 scores with other therapists familiar with the measure should help point out inconsistencies that would need clarification. GMFM-88 training workshops are no longer available but a self-instructional CD ROM is available from Cambridge University Press (Ordering information available at Wiley-Blackwell Publishing). This program provides useful training tips and allows assessors to work through several examples of each GMFM-88 item.

How long does it take to learn the GMFM-88 items?

The time to learn the GMFM-88 varies with the skill of the assessor, familiarity with standardized assessments and comfort and rapport with children with cerebral palsy. It takes a minimum of 3 hours to read through the manual and an additional 3 or more hours to work through the CD ROM training.

How long does it take to administer and score the GMFM-88?

Administering the GMFM-88 may take approximately 45-60 minutes for someone familiar with the measure, depending on the skill of the assessor, the ability level of the child (the more they can do the more items need to be tested!), and the child’s level of cooperation and understanding. This time will increase if the assessor wants to evaluate the use of ambulatory aids and/or orthotics in addition to an unaided assessment. Sometimes 2 sessions are required to complete all of the items. Item scoring is completed at the time of test administration. Calculation of dimension and total scores takes approximately 5 minutes with a calculator.

For what ages has the GMFM-88 been validated?

The original validation sample included children 5 months to 16 years old. The GMFM-88 is appropriate for children or adolescents with cerebral palsy or Down syndrome whose motor skills are at or below those of a 5–year old child without any motor disability.

Has the GMFM-88 been tested with, and found valid and reliable, for adults with cerebral palsy?

We are unaware of work done with adults; however the GMFM-88 has been used with adolescents. The GMFM-66 would likely be a more appropriate measure than the GMFM-88 for adults because not all items need to be assessed to get an accurate estimate of gross motor function.

Can the GMFM- 88 be used for children with diagnoses other than cerebral palsy?

While the GMFM-88 was designed and validated for children with cerebral palsy, there is evidence that the GMFM-88 version of the measure is also valid for use with children with Down syndrome. (Note: the GMFM-66 is only valid for children with cerebral palsy, because the scaling was developed with data only from children with cerebral palsy.) Because the GMFM-88 samples motor skills that are typical of normal developmental milestones, it may be useful for children other than for those with whom

it has been validated (i.e. children who have had a brain injury); however, reliability and validity should be established prior to using it with other groups of children.

Are there guidelines for administering the GMFM-88 in the home or community settings?

No there are no guidelines for the home setting. Any modification to the equipment should be as close as possible to the recommended equipment and documented to ensure consistency with testing over time.

How accurate is an obtained total score using the GMFM-88?

It is important to recognize that every time an assessor completes an evaluation with an individual child, the obtained total score is an estimate of the child’s gross motor function. The GMFM-88 does not provide a way for a therapist to determine how accurate (or error free) the obtained score is. However accuracy is increased by minimizing variation in: (1) the assessors (i.e. training to be reliable users), (2) the child (i.e. ensuring the child is comfortable and rested) and (3) the environment (i.e. in the same room, with the same equipment).

How frequently should the GMFM-88 be administered?

There are no guidelines provided about frequency of administration. Considerations include, but are not limited to: (1) age (more frequent evaluations in younger children), (2) type and intensity of intervention over a specified period of time (pre- and postevaluations around interventions that are expected to make a difference), (3) estimate of the amount of time that the child will require to learn a gross motor function(s), (4) concurrent health status (evaluation around the time the child experiences other health concerns to establish the impact on gross motor function), (5) a facility’s administrative requirement for an annual evaluation, and (6) responsiveness of the GMFM-88. Responsiveness of the GMFM-88 has been shown over a 6-month time interval and generally is more responsive to change for children under 3 years old.

How can change in GMFM-88 scores be interpreted?

Because of the tremendous variation among children with cerebral palsy, the magnitude of change that is considered clinically “important” for an individual child will vary, and will depend on the judgements made by the child, parents, and/or therapist. In the original validation work with the GMFM-88, parents and therapists have identified a gain of about 5 and 7 percentage points respectively, as being a “medium” positive change. The Gross Motor Function Measure (GMFM-66 and GMFM-88) User’s Manual has an appendix of average change scores for children of varying ages and GMFCS levels over six and twelve month intervals receiving intervention at children’s rehabilitation centres in Ontario, Canada. For interpretation of change on the GMFM-66 see the FAQs related to the GMFM-66.

FAQs relating to the GMFM-66

What is the GMFM-66?

The GMFM-66, or Gross Motor Function Measure 66, is an update of the GMFM-88 (the GMFM-66 is, in fact, the GMFM-88 minus 22 items!). It includes 66 items identified through Rasch analysis, which, together, best describe gross motor function in children with cerebral palsy of varying abilities. Like the GMFM-88, it is used to evaluate change in gross motor function over time or with intervention in children with cerebral palsy. The items are administered in the same way as with the GMFM-88 except for the scoring of the GMFM-66 where it is important to differentiate a true score of “0” (child does not initiate) from an item that is Not Tested (NT). This new measure uses a computer program (called the GMAE or Gross Motor Ability Estimator) to convert scores and plot them on an interval scale of gross motor function as opposed to the ordinal scaling of the original GMFM-88. It is valid only for use with children with cerebral palsy.

Who can use the GMFM-66?

The GMFM-66 was designed for use primarily by physical therapists who are familiar with children with cerebral palsy, and the administration and scoring criteria outlined in the manual.

What are the benefits of using the GMFM-66? 

It takes less time to administer the GMFM-66 as it contains 22 fewer items than the original GMFM-88 version. It can be scored using a computer program (GMAE have interactive link/”hot” button here) that provides interval scaling of items and allows plotting of scores on an item map. Item maps (interactive link/”hot” button) provide information that should allow you to determine what skills are likely to be next in the child’s development, thus assisting with goal setting. The computer programme assists in interpreting both clinically and statistically significant change over time by providing item maps and a summary of GMFM-66 scores (along with the 95% confidence intervals) over subsequent assessments. Another benefit includes the ability to get an accurate estimate of a child’s GMFM-66 score even when all items have not been administered.

How long does it take to learn the GMFM-66 items and the computerbased scoring system (GMAE) initially?

The length of time to learn the items of the GMFM-66 varies with the skill of the assessor, their familiarity with standardized assessments in general, and with the GMFM-88 in particular, and their comfort and rapport with children with cerebral palsy. It takes a minimum of 3 hours to read through the manual and an additional 3 or more hours to work through the CD ROM training. Learning how to score and interpret the GMFM-66 using the GMAE will require additional training. The length of time to learn the scoring system depends on the assessor’s familiarity with item maps.

How long does it take to administer, score and interpret the GMFM-66 for a child with cerebral palsy?

As with the GMFM-88, the length of time to administer the GMFM-66 depends on factors such as the skill of the assessor, the range of abilities of the child and the child’s level of cooperation and understanding during the assessment. Administering the GMFM-88 takes on average 45-60 minutes and this measure has 22 fewer items. We are currently documenting the administration time from therapists using the GMFM-66 in a trial with adolescents. Scoring for the GMFM-66 requires entering the item scores into a computer program and pushing a button to receive the GMFM-66 score, item maps and summary tables. Additional time is necessary to review and interpret item maps.

Do I need to administer all 66 items of the GMFM-66?

Work is currently being conducted to test algorithms for item subsets in each of the five levels of the GMFCS. At this point, it is best to test all 66 items.

Are the dimension scores calculated somewhere by the GMFM-66?

No. Item difficulties can be displayed by dimension on an “ item map by item order” but dimension scores are not available from the GMFM-66. Items can also be displayed in terms of difficulty using the “item map by difficulty order” which provides much richer information. Technically, the GMFM-66 doesn’t require all items to be tested so it is possible to focus on those items most relevant to the child negating the need for goal totals based on dimension scores. Accuracy of administering fewer items is currently being determined.

How accurate is an obtained total score using the GMFM-66?

As for all measurements, each time an assessor completes an evaluation with an individual child, the obtained total score will be an estimate of the child’s gross motor function. The GMFM-66, when used with the GMAE, automatically provides a 95% confidence interval (CI) around an obtained score. For example, a child might obtain a total score of 42, with a 95% CI of 39 to 44. This means that the therapist can be 95% confident that the child’s true score is somewhere between 39 and 44, and that the estimate on the day of testing was 42.

How frequently should the GMFM-66 be administered?

There are no guidelines provided about frequency of administration. Considerations include, but are not limited to: (1) age (more frequent evaluations in younger children), (2) type and intensity of intervention over a specified period of time (pre- and postevaluations around interventions that are expected to make a difference), (3) estimate of the amount of time that the child will require to learn a gross motor function(s), (4) concurrent health status (evaluation around the time the child experiences other health concerns to establish the impact on gross motor function), (5) a facility’s administrative requirement for an annual evaluation, and (6) responsiveness of the GMFM-66. Overall, the responsiveness of the GMFM-66 has been shown to be similar to that of the GMFM-88 over 6 and 12 months, however the GMFM-66 is more sensitive to change at the extremes of the scale (i.e. for those children scoring very low and those scoring very high) and probably less than the GMFM-88 for those children functioning in the middle of the scale .

How can change in GMFM-66 scores be interpreted?

The printout using the GMAE scoring program can be used to determine if change has occurred that is greater than measurement error. Basically, one needs to find out if the 95% confidence intervals (CI’s) (see also frequently asked question “How accurate is an obtained total score using the GMFM-66?”) between the first and second test occasion overlap. If they overlap, the difference in the obtained scores may be due to measurement error. If they do not overlap, the difference can be interpreted as true change. The overall magnitude of change in GMFM-66 score that is considered “clinically important” has not been determined scientifically but the therapist can use their clinical judgement to determine if the items showing improvement are clinically important for the child they are seeing.

FAQs relating to the differences between the GMFM-88 and the GMFM-66

What are the differences between the GMFM-88 and the GMFM-66?

The GMFM-88 is the original version of the Gross Motor Function Measure. It has 88 items that are grouped (for ease of clinical administration) into five dimensions. Scoring is done by calculating a percent score for each of the dimensions and an overall score averaging the five dimension scores. It has been traditionally assumed that a change score of ‘X’ units (%) over time had the same meaning across the whole GMFM88.

The GMFM-66 uses 66 of the original 88 items, assessed and scored in the same way as the GMFM-88, with the exception that on the GMFM-66, one has the option of scoring “not tested”. Apart from the fact of being somewhat shorter, the major difference between the two measures concerns the ‘scaling’ of the GMFM-66. Using a method of scaling called Rasch (‘item response theory’) analysis, it has become possible to describe the order of difficulty of all 66 GMFM items; to create an ‘item map’ that displays the relative level of difficulty of each step of each item; and to provide an ‘interval-level’ measure. This means that a change of ‘X’ points on the GMFM-66 has the same meaning anywhere on the scale – something that is not true with the GMFM88. From a clinical perspective it is possible to identify relatively easier and more difficult ‘next steps’ for any child whose gross motor function has been assessed with the GMFM-66.