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13.1)
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13.1)
To adequately describe the relationship between physical
activity and health, a researcher requires an objective and reliable method to
assess physical activity in subjects. Many different methods have been developed
over the years to measure physical activity and methods should be evaluated
using the following criteria:
·
Time periods are long enough to be representative
of normal daily life
·
There is minimal discomfort to the subjects
·
Technique is applicable for large populations
There are numerous methods to measure physical activity but
most fall into these categories:
·
Behavioral observation
·
Questionnaires (including diaries, recall
questionnaires and interviews)
·
Physiological markers (heart rate, calorimetry
and motion sensors)
Direct observation
Direct observation of physical activity was one of the earliest methods to assess physical activity.
This method uses trained raters to systematically record physical behaviors of participants in a restricted environment, such as a physical education class, school playground, or in the workplace.
Usually a prepared form or application is used to record the mode of
activity and some expression of intensity of energy expenditure at regular
intervals.
The biggest advantage of direct observation is that it provides more detailed information than perhaps any other methods.
Trained observers also are able to evaluate physical activity more objectively than participants themselves, especially when studying children.
The information
obtained from direct observation is more complete than any other method; however
there are several disadvantages such as:
·
High cost
·
Accuracy dependent on rater training and ability
·
Intrusive and may alter behaviors
·
Only certain environments can be studied
Direct observation is costly due to initial rater training expenses and the time for the rater to do the evaluation.
The accuracy of the rating is dependent on the rater training and ability and if multiple raters are used for a study, an analysis of intra-rater reliability is necessary.
Direct observation is more intrusive than other methods and can alter individual behaviors if the subjects know that they are being studied.
Additionally, since only restricted environments can be studied for a relatively short period of time, this sampling may or may not be characteristic of a typical day or week.
Although there are several disadvantages, direct observation is used regularly
as a method to gather physical activity data on small, sample populations.
Questionnaires
Questionnaires are by far the most common method used to assess physical activity.
This method is inexpensive and can be administered to large populations, however the reliability and validity of some questionnaires is low.
Before deciding on an instrument, make sure to research the reliability and validity for the questionnaire in your target population.
If you develop your own questionnaire, take the time to study the reliability and validity to ensure you can obtain good data.
There are several different methods commonly
called questionnaires including diaries, recall questionnaires and
interviews.
Diaries have a high participant burden but they are capable of obtaining frequency, intensity, duration, mode, and energy expenditure data on each subject.
These diaries require the subject to record their physical activity at regular intervals during the evaluation period.
For accuracy, the subjects should record activity as it happens or shortly thereafter.
Various modes of physical activity can be recorded and can be adapted quickly as new activities are introduced.
The main disadvantages to diaries are the subjects themselves.
Subject motivation can vary during the evaluation period and recording data may not be consistent.
As with many
self-report methods, diaries can be influenced by social desirability. The
subjects can be influenced by society and record in their diaries activity
levels that they should be performing, not what they actually performed during
the study period.
Recall questionnaires have the advantage that they do not influence actual activity levels during the evaluation period and can be self-administered or completed by a parent.
A wide variety of physical activity recall questionnaires exist, covering a wide variety of time periods, such as a typical week, previous week, or last month.
Since recall questionnaires are self-administered, they are relatively inexpensive to complete and a large population can be evaluated at similar time points.
Accuracy of physical activity recall can be an issue for recall questionnaires.
Depending on the recall period (ranging from a previous day to last week to a
lifetime) accuracy declines because subjects will not be able to recall every
activity for each time period.
Interviews are similar to recall questionnaires except a trained researcher is administrating the instrument.
This increases the accuracy as the interviewer can answer subject questions or ask follow up questions when answers are not complete.
Interviews are more labor
intensive, thus this method is more costly and requires more training than
self-administered questionnaires.
Figure 13.1
Common location for utilizing a questionnaire.
