Soc Sci Med. 2011 (Jun); 72 (11): 1826–1837 ~ FULL TEXT
William P. McDonald, MS Ed, DC, Keith F. Durkin, MS, PhD, and Mark Pfefer, MS, DC
Cleveland Chiropractic College,
Kansas City, MO.
For the past 100 years, chiropractic leaders in North America vigorously debated (1)
whether the profession’s scope of practice should be restricted to the examination and
adjustment of the spine or expanded to include a broad range of procedures from physical
and general medicine and (2) whether the spinal adjustment is or is not an effective
treatment for many early-stage visceral conditions. While leaders debated, the opinions of
practicing chiropractors were never systematically surveyed. This probability survey seeks
to ascertain the opinions of practicing chiropractors on the issues and questions that arise
from the historic conflict between broad scope advocates and focused scope proponents.
This is a systematic random attitudinal survey of 1,102 practicing chiropractors selected
from a mailing list of 60,409 names from Canada, Mexico, and the United States. The 687
respondents (63.3% response rate) produced four major findings: (1) numerous survey
items repeatedly show that >75% of the survey subjects favor a broad scope of clinical
services, (2) several items show that >75% of the respondents empirically find that the
adjustment of the vertebral subluxation complex usually elicits improvements in select
visceral ailments, (3) majorities of self-labeled broad scope, middle scope, and focused
scope chiropractors agree on all but one issue, and that is (4) respondents divide rather
evenly on the question of limited prescription rights for the profession. Practicing chiropractors
in this survey form a consensus on many scope of practice and philosophical
issues, in contrast to the history of conflict among leaders in the profession.
Key Indexing Terms chiropractic, chiropractors, survey, scope of practice
From the FULL TEXT Article:
For much of the past century, a variety of educators and
leaders in the chiropractic profession engaged in a robust
and, sometimes, fractious debate on clinical and philosophical
issues. This ongoing debate—coupled with little or no
survey feedback from practicing chiropractors—forges the
prevailing hypothesis: chiropractors are divided on the salient
questions, are clustered into rival camps, and practice in
divergent ways. Much of the profession’s tug-of-war is documented
in Peterson and Wiese’s history text.1
The purpose of this survey is to ascertain the attitudes of
North American chiropractors on the more contentious aspects
of scope of practice and philosophy. The primary goal is
to ascertain the degree to which the profession is, or is not,
Despite sporadic public discord among the profession’s
institutional leaders, the working hypothesis for this survey is
that most practicing chiropractors display considerable unity
in the way they think on the issues and practice in the clinic.
The assumption is that, while there are those who disagree on
various aspects of chiropractic, a consensus exists on most of
the key issues.
This is the first probability survey of North American chiropractors.
Previous surveys of this type in North America
were restricted to chiropractors in specific organizations and
jurisdictions or were hampered by low response rates. Other
large attitudinal surveys were of the nonprobability variety.
A survey of Canadian chiropractors finds 19% rejecting traditional
chiropractic philosophy, 22% endorsing traditional
chiropractic tenets, and 59% taking a moderate stand.2 It
should be noted that this survey suffers from unfortunate
wording in some of the belief statements to which the respondents
are asked to agree or disagree (5-point scale). The most
egregious wording is found in this belief statement: “The
scope of chiropractic practice should be limited to musculoskeletal
conditions” (italics added).2 Practice is the wrong
This specific debate among chiropractors has focused on
whether the vertebral adjustment should be limited to musculoskeletal
conditions. After all, chiropractors from all
points on the continuum have historically treated visceral
conditions. For example, broad scope (“mixer”) chiropractors
have used vitamins, herbs, homeopathic medicines,
biofeedback, exercises, etc., in an attempt to restore health in
visceral ailments. Likewise, focused scope (“straight”) chiropractors
have adjusted the vertebral subluxation in an attempt
to normalize nerve activity to ailing visceral tissues. In
short, the essence of this issue is about whether adjusting the
subluxation actually contributes to healing and the correction
of visceral dysfunction.
In a cross-sectional, practice-based study of 161 chiropractors
who treat an above average percentage of visceral
conditions, Hawk et al.3 found that 10.3% of the chief complaints
involve nonmusculoskeletal conditions. Thus, even
among practitioners with an interest in treating nonmusculoskeletal
conditions, the proportion of patients seeking such
care is relatively low.
In a randomized sample of U.S. chiropractors (658 respondents,
44% response rate), Rupert4 found that periodic maintenance
care is recommended to 79% of chiropractic patients
and that 34% comply. The article noted that 90% of the
chiropractors agreed or strongly agreed that optimizing
health was one of the purposes of maintenance care.
In a deft think piece on the rationale for chiropractic as a
profession, Hawk writes: “[The adjustment] must be informed
by a unique approach to healing and health that is
distinct from, although not necessarily at odds with, the medical
model. For it is the philosophy, the intuitive knowledge—
the belief system—that differentiates a complete system
from a procedure.”5
Of 753 chiropractors randomly sampled (65% response
rate) by Hawk and Dusio,6 90% see themselves as primary
care practitioners, 78% recently made referrals to MDs and
DOs, and 71% perform a complete health history on every
This postal survey reflects the opinions of respondents from
Mexico, all major regions of Canada, and all 50 states in the
The Ohio Northern University Institute for Social Research
provided advice and counsel prior to mailing the survey instrument
and, later, performed the data analysis. A draft version
of the survey was pretested on a nonrandom sample of
35 chiropractors. Revisions were then made to the survey.
The final sample was generated using Dynamic Chiropractic’s
60,409 names, including 56,026 U.S. chiropractors,
4,324 Canadian chiropractors, and 56 Mexican chiropractors.
The names on each of the three national lists were in zip
code/postal district order. The three national lists (strata)
were then linked (not combined) to make one master list.
After a random start, every 54th name was selected from this
master list to produce a systematic random sample of 1,102
chiropractors. This sampling pool contained 1,024 U.S. chiropractors,
76 Canadian chiropractors, and 2 Mexican chiropractors.
The systematic methodology (every 54th name),
when combined with a random start and lists arranged by zip
code, gives every name a known probability of selection
while ensuring geographic diversity.7
Of the 1,102 surveys mailed, 16 were returned from the
post office due to invalid addresses. From the 1,086 surveys
with valid addresses, 687 surveys were mailed back by respondents.
This translates into an overall response rate of
63.3%. This response rate compares favorably with large
probability surveys of health care practitioners. Three examples:
Job Analysis of Chiropractic8 produced a response rate of
43%; “Canadian Chiropractors’ Attitudes Towards Chiropractic
Philosophy and Scope of Practice”2 produced a response
rate of 68.3%; and “A National Survey of Primary
Care Physicians”9 produced a response rate of 62.7%.
Thirty-two surveys were excluded from the final analysis
for one of the following three reasons: (1) the respondents
indicated they were no longer practicing chiropractors (n
7); (2) surveys were received after data analysis had commenced
(n 4); and (3) the majority of a survey was incomplete
(n 21). It is a common practice to exclude surveys
that have large amounts of missing data or invalid responses
There are basically four types of errors that can flaw a
probability survey: coverage error, sampling error, measurement
error, and nonresponse error.13,14
Attempts were made to minimize coverage error by using
the largest available mailing list (Dynamic Chiropractic’s
60,409 names) and using selection methodology to give each
name a known probability of being included in the sample.
Sampling error was minimized by insuring that a large
number of names were selected (1,102), which netted 687
respondents, of which 655 survey instruments were usable.
Measurement error, which results from such things as unclear
questions and impossible answers, was addressed in
several ways. The questions were critiqued by 11 individuals,
primarily chiropractors and social scientists. The questions
were field tested with 35 chiropractors who were asked to
provide feedback about the questions after they completed
the survey; changes were made in the survey based on the
field testing. Once the official survey was conducted, 21
questionnaires were discounted because of failure to complete
large amounts of the survey. The returned survey instruments
were reviewed for answers that were impossible or
did not follow instructions.
Nonresponse error appears when there is a marked difference
in the type of people responding and not responding. A
geopolitical breakdown of the respondents shows that all
regions responded adequately:
(1) Eastern United States produced 46.6% of the respondents (vs. 49.6% of the original sample),
(2) Western United States yielded 45.2% of the respondents (vs. 43.6% of the sample),
(3) Canada produced 8.0% of the respondents (vs. 6.5% of the sample, and
(4) Mexico yielded 0.3% of the respondents (vs. 0.2% of the sample).
Surveys with a response rate below 60% are more prone to nonresponse error.7,15
For those variables that were measured on a scale, the
mean is reported as the measure of the central tendency and
the standard deviation is reported as a measure of variability.
For those variables that were measured at the nominal
level, the 95% confidence interval is also reported. This indicates
that one can be 95% certain that the actual number
lies within the reported range of values.16
For those relationships involving variables measured at the
nominal level, the Chi-Square test for independence was
used. A significant result for this test suggests that the frequency
distribution for one variable is related to (or dependent
on) the categories for the second variable and the two
are thus correlated.17,18
For those relationships in which the dependent variable
was measured on a scale, a statistical procedure called an
Analysis of Variance (ANOVA) was used to compare the
mean scores. A significant result for the ANOVA test indicates
that the observed differences in the mean scores are unlikely
due to chance.18 However, when the independent variable
has three levels, it is necessary to use a second “post-hoc” test
to determine which precise mean scores are significantly different.
In those instances, the Fisher LSD (least significant
difference) test was utilized. This is an appropriate test when,
as is true in this study, there are only a few variables being
The survey subjects were divided rather evenly in terms of
their years in practice: 34% (≤10 years), 35% (11-20 years),
and 31% (≥21 years). The ages of respondents included 32%
who were ≤39, 61% who were 40-59, and 8% who were
≥60. Males made up 66% of the subjects.
In their day-to-day practice, 23% reported using one of the
traditional-force spinal adjusting techniques, 10% claimed
one of the low-force methods, and 67% indicated they employ
both approaches. Nearly 90% of the subjects owned
their practice, while 10% did not. The respondents came
from practices of varying sizes: 46% personally treat ≤99
patients weekly, 30% treat 100-149 patients per week, and
24% see ≥150 each week. Annual net income for the survey
subjects also varied: 56% made ≤$99,999, 24% earned
$100,000 to $149,999, while 20% netted ≥$150,000.
The level of prechiropractic education included 66% with
a bachelor’s degree or higher, 17% with an associate’s degree,
and 16% without a degree. Prior to attending chiropractic
college, 22% of those surveyed had a relative or family member
who was a practicing chiropractor. Before enrolling in
chiropractic school, 76% had been under the care of a chiropractor
at one time or another.
The survey subjects included alumni from 18 chiropractic
colleges in North America, in additional to several other chiropractic
schools. The eight largest alumni groups included
graduates of Palmer (Davenport) 23%, Life (Marietta) 11%,
National 10%, Logan 7%, New York 7%, Canadian 6%,
Northwestern 5%, and Southern California 5%.
The philosophical distribution of the respondents is presented
in Table 1. Using the three definitions below, they
self-rated their personal clinical philosophical positions on a
Broad Scope allows a wide array of manual and other clinical
procedures for diagnosing and treating both symptoms
and neuromusculoskeletal conditions. Some in this camp
would include minor surgery, obstetrics, and prescribing
Middle Scope tends to combine subluxation adjusting with
other conservative treatment and diagnostic procedures.
Focused Scope emphasizes the detection and adjustment of
vertebral subluxations to restore normal nerve activity to
musculoskeletal and visceral tissues. Some in this camp oppose
therapeutic modalities, extremity adjusting, and diagnostic
By collapsing the data in Table 1, we see that the respondents
make up three broad philosophical groupings: middle
scope (46.4%), broad scope (34.3%), and focused scope
In response to the question, “Should chiropractic retain
the term vertebral subluxation complex?,” the respondents
(n = 638) overwhelmingly voted to do so: 88.1% yes (95%
confidence interval 85.5-90.7), 11.9% no (95% CI 9.3-14.5).
To the question, “Should the adjustment be limited to
musculoskeletal conditions?,” 89.8% of the respondents (n = 646) answered no (95% CI 87.4-92.2) and 10.2% yes (95%
Given the question, “In what percentage of visceral ailments
is the vertebral subluxation a significant contributing
factor?,” the respondents gave a mean response of 62.1%. In
short, the respondents, as a group, are of the opinion that the
subluxation contributes to about 6 of every 10 visceral ailments.
The 26.0 standard deviation indicates a wide dispersal
of responses, including these two statistically extreme
attitudes: 10.9% believe the subluxation contributes to 100%
of all visceral ailments, and 1.5% believe the subluxation
never contributes to visceral ailments.
When asked, “Do adjustments usually elicit improvements
in the following cases?,” a majority of the respondents answered
in the affirmative for four select conditions:
(1) migraines (n = 633): yes 89.3% (95% CI 86.8-91.8),
(2) dysmenorrhea (n = 602): yes 84.2 (95% CI 81.2-87.2),
(3) otitis media (n = 586): yes 77.0% (95% CI 73.5-80.5), and
(4) allergic asthma (n = 604): yes 75.5% (95% CI 72.0-79.0).
North American chiropractors in this survey perform a
broad spectrum of clinical services and practices (Table 2).
Given a list of 24 clinical services, procedures, and privileges
that are utilized by some chiropractors, a majority of the
respondents deemed 21 of them to be “appropriate for the
chiropractic profession’s scope of practice” (Table 3). Before
reviewing the list of 24 services, the respondents were instructed
to assume that any chiropractor who would choose
to offer one of the services would have received “adequate
Except for a few jurisdictions in the world, chiropractic has
traditionally presented itself as a drugless, nonsurgical health
care profession. Given this background, it is not surprising
that North American chiropractors, as a group, are of the
opinion that only 39.8% of all pharmaceutical prescriptions
filled annually are clinically beneficial. Yet, a slight majority
(54.3%) think chiropractors should be permitted to write
over-the-counter (OTC) prescriptions. On the other hand, a
slight majority (51.2%) oppose the proposition of chiropractors
writing prescriptions for musculoskeletal medicines
(e.g., muscle relaxants). Finally, an overwhelming majority
(88.6%) oppose chiropractors writing prescriptions for any
and all medicines, including controlled substances.
Chiropractors with the smaller practices were significantly
more supportive of the right to prescribe OTC medicines:
60.7% of smaller (≤99 visits weekly) practitioners favored
the right to prescribe OTC medicines, in contrast to 48.9% of
moderately sized (100-149 visits) practitioners, and 50.3%
of large (≥150 visits) practitioners (p < 0.05).
Respondents who see smaller numbers of patients also
differ on the results they report from the spinal adjustment.
In acute mechanical lumbar cases, the practitioners were
asked to rate the spinal adjustment on an effectiveness scale
of 0 (no benefit) to 10 (great benefit): the small practitioners
rated the adjustment at 8.8, while in contrast the moderate
and large practitioners rated the adjustment at 9.2 and 9.3,
respectively (p < 0.05).
While 69.8% of the smaller practitioners found the adjustment
usually elicits improvements in allergic asthma, in contrast,
77.8 and 83.6% of the moderate and large practitioners
found the adjustment usually elicits improvements in the
same type of asthma (p < 0.05).
Nearly one-fourth of the respondents had not been treated
by a chiropractor before entering chiropractic college. These
respondents rated the effectiveness of the adjustment in typical
acute mechanical lumbar cases as being 8.7 (10-point
scale), while others in the survey rated it as 9.1 (p < 0.01).
Similarly, of those who had not been a chiropractic patient
before entering chiropractic school, 68.1% found the adjustment
usually improves allergic asthma cases, while 78.0% of
the other respondents usually found improvement in these
cases (p < 0.01).
Using the three largest alumni groups in order to minimalize
sampling error, the respondents who attended National
(n = 63) had the highest proportion who self-labeled themselves
as broad scope (57.1%), while Palmer (Davenport)
(n = 148) had the highest proportion who labeled themselves
as middle scope (55.1%), and Life (Marietta) (n = 69)
had the highest proportion who chose the focused scope
designation (31.9%) (p < 0.01).
There was a statistically significant relationship between
the self-rated scope of practice findings and each of the 10
dependent variables used in the bivariate analyses. This
means that the 9-point scope of practice scale and the accompanying
definitions (broad scope, middle scope, and focused
scope), taken together, constitute a powerful scope of practice
index. The most dramatic statistical association in the
entire survey was between the responses on the scope of
practice scale and the responses on the question of whether
chiropractors should be permitted to prescribe OTC medicines.
Among broad scope respondents, 77.1% indicated yes,
while 53.5% of the middle scope and 17.6% of focused scope
respondents answered yes (p < 0.01).
One word that summarizes the findings of this survey: consenus.
Rank and file chiropractors of North America line up in
supermajorities (>75%) to endorse the following key concepts:
1. The appropriateness of a broad spectrum of conservative clinical services,
practices, procedures, and privileges
2. The term vertebral subluxation complex
3. The subluxation as a significant contributing factor in many visceral ailments
4. The adjustment as an effective treatment procedure for both musculoskeletal
and selected visceral conditions
5. The differential diagnosis
6. The concept of maintenance/wellness care
7. The teaching of a relationship between spinal subluxations and visceral health
8. The counseling of patients in stress reduction and ergonomics
Middle scope chiropractors endorse the above eight concepts.
Even majorities of both broad scope and focused scope
respondents register support for each of these concepts.
Despite the fact that the respondents overwhelmingly endorsed
the term vertebral subluxation complex, some chiropractors
continue to criticize the terminology on several
counts. One complaint is that the profession sows confusion
by giving this medical concept a decidedly chiropractic twist.
When orthopedists say subluxation, they mean an acute
overriding of vertebral facets. Chiropractors, on the other
hand, often use the term to denote a fixation and/or slight
off-centering of one vertebra with another.
This fixation has traditionally been viewed by the profession
as causing sensory and motor nerve disturbances, as well
as sometimes contributing to altered autonomic activity,
hence, disposing patients to illness and visceral dysfunction.
Because this autonomic hypothesis is primarily empirically
based, some chiropractors argue it should not be presented to
Despite these very real concerns, the one-sided response
from the chiropractors in this survey indicates that, from the
perspective of field practitioners, the term vertebral subluxation
complex is more of a unifying term than it is a divisive
The question “Should the adjustment be limited to musculoskeletal
conditions?” is rejected by a 9 to 1 ratio and
stands as another indication that large numbers of chiropractors
hold the view that in select cases they have the clinical
potential to influence visceral conditions by adjusting the
It should be noted that in this question the term neuromusculoskeletal
was rejected for the more succinct musculoskeletal.
The term neuromusculoskeletal opens the door for
misunderstanding. To some broad scope chiropractors, this
term might be interpreted as being concerned only with
nerve activity as it relates to the musculoskeletal system. Yet,
to some focused scope chiropractors, the prefix neuro might
suggest both peripheral and autonomic nerve activity, with
the latter relating to the physiology of internal tissues.
While large majorities of the survey subjects indicated they
usually elicit improvements by rendering spinal adjustments
in four specific conditions (migraines, dysmenorrhea, otitis
media, and allergic asthma), it must be remembered that the
above results are based on the respondents’ general perception
of the clinical outcomes. Personal clinical experience,
obviously, is not the same as controlled clinical studies. Instead
of proving that adjustments benefit internal conditions,
these data simply document that large proportions of the
respondents believe that their adjustments have been effective
with select internal ailments.
Given the profession’s prevailing attitude that a majority of
prescriptions are not clinically beneficial, why would approximately
half of the survey subjects favor limited (over-the-counter and musculoskeletal) prescription rights? The
typical North American chiropractor cannot write prescriptions,
including OTC medicines. This causes a problem not
only for the chiropractor who would like to prescribe OTC
medicines, but it also causes a problem for the practitioner
who wants to get patients off the chronic use of some OTC
drugs (e.g., long-term use of Ibuprophen causing rebound
pain). It is the legal right to prescribe a class of medicine that
conveys the legal right to manage that same class of medicine.
Therefore, even the chiropractors who are opposed to pharmaceuticals
and wish only to counsel patients against OTC
medicines may find themselves arguing for limited prescription
The fact that 93.4% endorse the differential diagnosis at
new patient examinations is a clean break with the old proposition
that chiropractors should eschew all diagnosis in favor
of analyzing the spine for subluxations only. This finding,
when combined with the 74.2% who endorse hospital admitting
privileges, indicates that most in the profession no longer
narrowly define themselves in opposition to medicine.
The findings of this survey clearly suggest that the profession
needs to review and modify century-old stereotypes.
Most broad scope practitioners endorse the subluxation and
its somatovisceral implications. Most focused scope practitioners
routinely perform a differential diagnosis and offer
The profession probably needs to more fully appreciate
the fact that nearly one-half of the respondents choose to
place themselves near the middle of the scope of practice
Within the focused scope camp, particularly among the
more tradition-bound practitioners, there is a need to appreciate
the fact that the profession soundly rejects the old
notion that chiropractic should restrict itself to the adjustment
of the subluxation. These same chiropractors, however,
can be cheered by the fact that field practitioners
clearly acknowledge the contribution of the vertebral sublxuation
to a majority of visceral ailments. Still, this empirically
based proposition will never move from the realm
of philosophy to science until research findings sanction
Within the broad scope camp, especially among the more
doctrinaire practitioners, there is a need to appreciate the fact
that, while great numbers of chiropractors believe the subluxation
contributes to visceral ailments, they are not creedalists.
As a group, the respondents hold that the subluxation
contributes to approximately 6 of 10 visceral conditions, not
9 of 10 as may have been the case in the early 1900s. Otherwise,
these same broad scope practitioners can celebrate that
the profession clearly endorses the appropriateness of a
board spectrum of clinical services.
The one item that appears to divide chiropractors involves
limited prescriptions rights, be it over-the-counter medicines
or musculoskeletal pharmaceuticals. Even this issue may be
dampened by the profession’s overall skepticism as to the
clinical benefits of medicines; only 39.8% of all prescriptions
are viewed as beneficial.
One weakness in this study is that intensity of attitudes is
not measured. This was planned. The object was to limit the
survey instrument to one legal sheet, printed front and back,
so as to maximize the response rate.
Another weakness centers on the patients-treated-perweek
response category of 99 or less. Since almost 46% of the
respondents checked off 99 or less as the amount of patients
they personally treat each week, there is a clear need to create
a lower category. One possibility would be 49 or less.
The results of this survey suggest that North American
chiropractors are not only in consensus on many issues, but
are less defensive, less absolutist, and less polemic than the
stereotype. The data also indicate that chiropractors know
they offer patients a valuable service. The picture emerging
from this survey is of a confident, pragmatic, and discerning
profession, more capable than ever of participating in an
interdisciplinary health care environment.
Peterson D, Wiese G:
Chiropractic: An Illustrated History.
St. Louis, MO, Mosby, 1995
Biggs L, Hay D, Mierau D:
Canadian chiropractors’ attitudes towards chiropractic philosophy and scope of practice:
Implications for the implementation of clinical practice guidelines.
J Can Chiropractic Assoc 41:145-154, 1997
Hawk C, Long C, Boulanger K:
Prevalence of Nonmusculoskeletal Complaints in Chiropractic Practice:
Report From a Practice-based Research Program
J Manipulative Physiol Ther 2001 (Mar); 24 (3): 157–169
A Survey of Practice Patterns and the Health Promotion and Prevention Attitudes of US Chiropractors
Maintenance Care: Part I
J Manipulative Physiol Ther 2000 (Jan); 23 (1): 1–9
Chiropractic: More than spinal manipulation.
J Chiropractic Humanities 8:71-76, 1998
Hawk C, Dusio M:
Chiropractors’ attitudes toward training in prevention:
Results of a survey of 492 chiropractors on primary care and prevention-related issues.
J Manipulative Physiol Ther 18:57-64, 1995
Salant P, Dillman DA:
How to Conduct Your Own Survey.
New York, NY, John Wiley & Sons, 1994
Christensen M, Kerkhoff D Kollasch M, et al:
Job Analysis of Chiropractic 2000
Greeley, CO, National Board of Chiropractic Examiners, 2000
Parsons J, Warnecke R, Czaja R, et al:
Factors associated with response rates in a national survey of primary care physicians.
Eval Rev 18:756-766, 1994
Johnson MD, Jay MS, Shoup B, et al:
Anabolic steroid use among male adolescents.
Pediatrics 83:921-924, 1989
Marcos AC, Bahr SJ, Johnson RE:
Testing a bonding/association theory of adolescent drug use.
Soc Forces 65:135-161, 1986
Michaels JW, Miethe TD:
Applying theories of deviance to academic cheating.
Soc Sci Q 70:870-885, 1989
Weisberg H, Krosnick J, Bowen B:
An Introduction to Survey Research, Polling, and Data Analysis (ed 3).
Thousand Oaks, CA, Sage Publications, 1996
The Practice of Social Research (ed 5).
Belmont, CA, Wadsworth,
AMA Style Manual Committee:
American Medical Association Manual of Style: A Guide for Authors and Editors.
Chicago, IL, American Medical Association, 1998
Social Research Methods: Qualitative and Quantitative Approaches (ed 5).
New York, NY, Allyn & Bacon, 2003
Gravetter FJ, Wallnau LB:
Statistics for the Behavioral Sciences (ed 5).
New York, NY, Allyn & Bacon, 2000
Handbook of Parametric and Nonparametric Statistical Procedures (ed 2).
New York, NY, Chapman and Hall, 2000
Experimental Design: Procedures in Behavior Science (ed 2).
Pacific Grove, CA, Brooks/Cole, 1982
Return to the CHIROPRACTIC IDENTITY Page