June 28 - 29, 2007 Advisory Committee Meeting Minutes

Overview of Systematic Literature Review Approach

Dr. Kohl opened with an overview of four areas that will be covered in his presentation: the rational utilized in CDC's overall approach in gathering data, methodology in abstracting data, review how data was inputted and demonstrate the database live.

Due to the time constraints of producing Physical Activity Guidelines within a 2-year window, compared to the 5-year cycle for Dietary Guidelines, there was a need to make certain assumptions and decisions, before the formation of the Advisory Committee, in order to prepare data that can be reviewed immediately. Three goals guided the CDC: Develop and implement a feasible approach for systematic review of physical activity and health literature for maximal benefit to the Federal Advisory Committee, provide an initial literature database in preparation for first Committee meeting and support the Committee throughout its term.

The actual literature review is organized in four phases. The first phase is a developmental phase that began in October 2006 which included resource gathering and planning. Phase A is the initial literature review conducted by CDC and subsequently Phase B will be the reactive phase starting at the end of this Committee meeting through the next meeting in December. During Phase B, Committee members will review the data, comment and request additional data. Phase C, December – February, is the final phase wrapping up work in preparation for the Committee's report to HHS.

The framework for the literature review consists of six exposure types as they relate to eight health outcome areas. The exposures include intensity, frequency, duration, pattern, type and an estimate of caloric expenditure. The outcomes include cardiovascular-respiratory health outcomes, metabolic health outcomes, musculoskeletal health, cancers, functional health, mental health, all-cause mortality, and adverse events and risks of physical activity. Additionally, the groups were broken down by age, children and adolescents (ages 6 – 18), adults (ages 19 – 64) and older adults (ages 65 and over) and were reviewed functionally by three teams consisting of Quality Control, an External Science Advisory Group — providing input on constructing the searches, and the Scientific Review Team aided by a contractor responsible for database systems development and outside data abstractors.

While it may have been preferable to pull all literature starting from 1953 it was apparent that would not be possible so the search started 1 year prior to the 1995 Surgeon General's Report and goes through 2006. Functionally, a fourth age group emerged — Mixed Ages — to account for studies that have very large data sets or account for studies that occur over very long periods of time.

Again, due to the proactive approach of this strategy the CDC team could not wait for research questions to come from the Committee so four questions were framed to allow the process to move forward:

  1. Is physical activity associated with an outcome?
  2. What is the evidence of the dose of physical activities associated with a certain outcome?
  3. What is the evidence that physical activity actually might increase the risk of a certain outcome?
  4. What is the evidence in exposure of physical activity, other than 30 minutes per day, associated with an outcome?

Additional research questions from the Committee are possible.

In order to manage a very large amount of data an 8-step process was devised to manage the abstracting process:

Develop Search Strategy
A professional library scientist and an external scientific advisory group assisted in the development of key strategies. Through this process the group unearthed idiosyncrasies working with Medline and search terms such as key words, exploded terms and mesh headings.

Execute Search Strategy
In early January the strategy was implemented to come up with reference lists. The material that made up the universe of literature from 1995 – January 2007 was immense.

Abstract Retrieval
Data inputted into literature reference manager systems and retrieved for triage analysis.

Abstract Triage
Abstracts were reviewed to determine if they were relevant and if they met pre-determined exclusion criteria. Excluded abstracts were filed away while other abstracts were flagged for retrieval and coding. If an abstract was not relevant towards diagnosable disease endpoints, with some exceptions, were excluded and or deferred to Phase B. All studies including body composition were included along with risk and adverse events dealing only with variability in physical activity exposure and functional health studies in older adults. Studies dealing with acute effects of single exercise bout were excluded.

Abstracts that met the following criteria were deferred to Phase B.

  • Risk factors or risk markers as outcomes
  • Physiologic adaptations without health outcome
  • Fetal outcomes
  • Balance – except where appropriate for functional health in older adults
  • Addictive behaviors
  • Cognitive function in youth

The primary reasons for exclusion included 14% excluded due to inappropriate format, 27% excluded because of no health outcome and 59% excluded because there was something wrong with their physical activity exposure data. Of 12,428 papers reviewed, 1,105 papers were abstracted.

Paper Retrieval
1,105 papers were recorded on DVD and sent to the Committee.

Assignment to Abstracters
In order to properly enter and code data into the database 49 individuals that were masters-trained, exercise-students or professionals with public health expertise were recruited and trained.

Coding of Papers
As papers were coded a quality assurance program was implemented to insure accuracy. To get a sense of the quality of work performed 14% of the papers were selected to undergo "double coding."

Database Development
The strengths of the initial database include its specific focus on physical activity and its ability to focus on multiple outcomes. It is standardized, systematic and very searchable. The database is dynamic meaning additional choices can be made and additional papers can be added. It is also very inclusive and not limited to one type of study. The database also links to the original PDF and strong quality assurance methods were employed in the vetting of abstracts.

At the conclusion of the presentation, members of the Committee were led through a hands-on demonstration of the database led by Susan Carlson from CDC and other CDC team members.

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