"We recommend that the annual check-up, as practised almost ritualistically for several decades in North America, be abandoned. We consider that the routine general annual check-up is nonspecific and casts a searching net far too broadly, particularly in the adult, is inefficient and, at times, is potentially harmful [2]."

The periodic health examination-the medical evaluation of ostensibly healthy adults, performed at regular intervals by physicians-has changed significantly over time. Since its conception by visionary clinicians, great shifts have occurred both in the legitimacy with which the periodic examination has been viewed by physicians and patients and in the ideal content of the examination. It has gone from being disregarded to being widely accepted to being cautiously endorsed and has evolved from a comprehensive fact-finding exercise aimed at detecting physical defects and amassing the available techniques of history taking, physical examination, and laboratory technology into a parsimonious collection of tests for the early diagnosis of disease.

What accounts for these historical shifts? A conventional view is that they reflect a positive evolutionary advance in knowledge-a replacement of naive enthusiasm with scientific skepticism. Many contemporary analyses of the early periodic health examination movement implicitly offer such a view, criticizing the movement as founded on insufficient evidence of the effectiveness of the periodic examination in preventing disease and death [3-5].

I present evidence for an alternative argument: that shifts in the acceptance and content of the periodic health examination were tied to fundamental changes in the objectives that the examination served. These changes, in turn, reflected the overriding concerns of the examination's strongest advocates at various points in history. By analyzing the writings of key figures in the periodic health examination movement, I define these objectives and concerns and show how they shaped the perceived legitimacy and content of the periodic examination. I argue that because evaluations of the periodic examination are determined by particular concerns, contemporary developments cannot be entirely viewed as evolutionary advancements and the forms and objectives of the examination require continual reevaluation. My analysis is limited primarily to developments in North America because the periodic health examination was debated and implemented most aggressively there.

The Periodic Health Examination through the 1960s

Conceptual Roots

The precise origin of the periodic health examination is unknown, but many writers trace its intellectual beginnings to British physician Horace Dobell, a renowned clinician, author, and expert on tuberculosis and diseases of the chest [6-8]. In 1861, Dobell outlined an argument for the periodic examination of ostensibly healthy persons [1]. Central to his thesis were the notion that diseases are preceded by "pre-existent physiological states" of "low health" and the idea that therapeutic efforts are more effective at these earlier stages. Dobell proposed the periodic health examination as a way to identify "these earliest evasive periods of defect in the physiological state, and to adopt measures for their remedy." He advocated an exhaustive history, a meticulous physical examination, and use of laboratory tests. The comprehensiveness of this exercise evinced the conviction that the slightest physiologic deviation had pathogenic relevance and that its detection would yield therapeutic power.

Similar ideas emerged in the United States at the turn of the century. Perhaps the first argument to appear in the literature was that of Philadelphia physician George Gould, an accomplished author and national Figure in the medical community. In an address at the Fifty-First Annual Meeting of the American Medical Association (AMA) [9], Gould proposed periodic "personal biologic examinations" as a method for gaining scientific knowledge of the early natural history of disease. He advocated comprehensive periodic examinations as a way to gather as much data as possible to enable physicians to affect the course of disease.

Other early versions of the periodic health examination, although comprehensive in content, were concerned with finding specific physical conditions. Periodic examination of school children was advocated in the late 1800s and early 1900s as a way to detect physical impairments and contagious diseases [10-12]. In 1915, the National Tuberculosis Association designated a week for all persons to have a general physical examination; this popularized annual examinations as a tool for the early diagnosis of disease in general and tuberculosis in particular [13, 14]. Periodic examinations were also proposed as a promising tool in the fight against cancer. As early as 1918, when little was known about cancer, many prominent physicians advocated annual examinations specifically for the detection of cancer in the hope that early diagnosis would increase the probability of cure [13].

The innovative intellectual orientation toward early diagnosis and physiologic states preceding manifestations of disease provided the conceptual roots for the early periodic health examination movement. The guiding concerns of early proponents were scientific and humanitarian, and the periodic examination was meant to advance knowledge and prevent diseases that had yet to be fully understood or effectively treated; the content of the examination was thus all-encompassing.

Economic Concerns

The Life Insurance Industry

Developments outside of clinical practice proved more influential than early intellectual concepts in promoting the periodic health examination. From as early as the mid-1800s, the life insurance industry had been interested in using medical history taking and physical diagnosis to assess the financial risk posed by life insurance applicants [15]. By the turn of the century, most major life insurance companies had set up medical divisions and were employing physicians to perform physical examinations. This practice became even more widespread and refined during the 20th century.

For insurance executives, it was a short conceptual leap from recommending one-time examinations for applicants to recommending periodic examinations for existing policyholders with the aim of decreasing their risk for death [8]. Such programs were implemented as early as 1909 under the direction of Eugene Lyman Fisk, an industry leader who became the most prolific advocate of the early periodic health examination. As medical director of the Life Extension Institute, an organization founded in 1913 to perform periodic health examinations for life insurance companies, Fisk had overseen more then 250 000 examinations by 1923 [8, 10, 16].

The enthusiastic implementation of the periodic health examination was supported by little published evidence of the examination's effectiveness, especially in the early years of the movement. Such evidence was first obtained in 1916. Analyzing data from the Life Extension Institute, Fisk compared the observed mortality of examined persons with their expected mortality according to actuarial calculation. He showed a relative mortality reduction that ranged from 18% with 9-year follow-up [6] to 53% with 5-year follow-up [7]. In 1921, A.S. Knight, medical director of the Metropolitan Life Insurance Company, reported that policyholders examined during 1914-1915 had had a 28% reduction in expected mortality over the subsequent 5 years [17]. The driving reason behind the insurance industry's willing acceptance of the periodic health examination, however, was the examination's profit-making potential. Metropolitan Life estimated that money invested in the practice would return profits of 200% in 5 years [7]. The mortality reduction demonstrated by Knight was projected to save more than $120 000 [18]. These data compelled industry leaders to accept and further develop the periodic health examination.

The profit motive also influenced conceptions of the ideal content of the examination. Because of its aversion to financial risk, the life insurance industry treated the physical defects of a policy applicant as significant until they were proven to be otherwise, a conservative stance that Fisk defended [19]. The periodic health examination thus became an exceedingly comprehensive search for physical defects, which were viewed as harbingers of disease and imbued with a magnified significance [6]. According to Fisk, proper detection of defects required painstakingly thorough history taking; head-to-toe physical examination; and multiple blood and urine tests, roentgenograms, electrocardiograms, and more [6, 20-22]. Upon finding that almost all ostensibly healthy persons had some form of impairment or physical defects-"more than 50 percent in need of medical or surgical attention" [21] -proponents concluded, using circular arguments, that periodic health examinations were justified.

The life insurance industry thus provided fertile ground for the growth of the periodic health examination movement. The industry's economic goals created a need for an instrument with which to assess and reduce the individual person's risk for death; this shaped a periodic health examination that was comprehensive and aimed at the detection of physical defects.

Private Corporate Industry

Private industry also fueled the periodic health examination movement from the early 1900s to mid-century, stimulating much empirical work and professional debate. A comprehensive U.S. Public Health Service review of the literature on the periodic health examination from the early 1900s through 1962 included 153 citations, almost half of which were analyses or reports of data from industrial settings; this type of report represented most articles published in the United States from 1940 onward [23].

Most of the published data from industrial medicine programs accrued at the time when or even years after such programs were already being promoted, and they focused on the prevalence of conditions revealed by periodic examinations rather than on the ability of the practice to reduce mortality, morbidity, lost work days, disability, or hospitalization of employees [24, 25]. As in the life insurance industry, the alacrity with which corporate industry accepted the periodic health examination reflected deep economic concerns that belied its ostensibly humanitarian goals. The passage of workers' compensation legislation in the early 1900s created a need to detect and monitor physical conditions that might predispose employees to injure themselves or others on the job [13, 25]. Other, broader needs were the improvement of productivity, morale, and operating efficiency. Industry embraced the periodic health examination primarily as an instrument for achieving these goals [24, 25].

Private industry also emphasized the detection of physical defects and advocated as thorough an examination as possible. The AMA Council on Industrial Health recommended a comprehensive survey that included a medical history, a detailed physical and mental examination, and use of available laboratory studies [26].

Corporate industry took a special interest in ensuring the health of its executives. "Executive physical" programs began in several corporations as early as the 1920s and spread rapidly [24, 27]. In the 1940s and 1950s, clinics devoted to executive physical examinations were created at private institutions and major academic medical centers. Typically, executive examinations were exceedingly thorough and liberal in their use of available diagnostic testing; the procedure at the famous Greenbrier Clinic, for example, was a 3-day, multisystemic diagnostic survey [28]. The rationale for such comprehensiveness was the importance of the executive's health to the success of the company [29].

In linking the health of employees to its economic goals, private corporate industry played a central role in advancing the concept and practice of periodic health examinations in the 20th century. The comprehensiveness of the examination was commensurate with what industry perceived to be the economic risks at stake in the health of its workers.

Professional Concerns: Organized Medicine

Organized medicine also played a major role in the development of the periodic health examination. In 1922, the AMA officially endorsed the periodic health examination and began a campaign to spread its practice. In 1923, an official report detailing the method of the periodic health examination was published in Journal of the American Medical Association [30] and the AMA published Periodic Health Examination: A Manual for Physicians, which was revised in 1932, 1940, and 1947 [31]. The National Health Council, in cooperation with the AMA, the U.S. Public Health Service, and state departments of health, began a nationwide campaign to promote periodic health examinations with the slogan "Have a Health Examination on Your Birthday" and a goal of achieving 10 million examinations in the year following 4 July 1923 [8].

The AMA based its endorsement on several objectives of the periodic health examination. Among these were early detection of disorders and disease; recognition of adverse environmental factors and living habits; and promotion of vigor, physical and mental fitness, and improved quality of life [30, 31]. But organized medicine had its own motives for promoting the periodic examination. Historian George Rosen argued that organized medicine saw the periodic health examination as serving the instrumental purpose of "enhancing the position of the practitioner in the community," particularly in the wake of its opposition to compulsory health insurance [13]. Prominent physicians emphasized that the periodic examination provided the opportunity to establish physician-patient relationships, thereby furthering the practice and influence of the physician in the community [8, 32].

The examination also served to assert the autonomy and influence of physicians vis-a-vis public health institutions and the government; this was a major professional agenda in the early and mid-1900s [12, 13]. Public health organizations and physicians attempted to control the periodic health examination. The medical community often opposed the implementation of health examination programs in schools and industry by municipal health departments unless the services of private physicians were enlisted [12]. Physicians in the 1950s zealously sought to lay claim to the practice of the periodic health examination [32, 33] and appealed to fellow physicians to perform examinations in order to avert government control of this and other endeavors [33].

Other Historical Influences

Other developments influenced the periodic health examination movement until the 1950s. Intellectual interest in preventive medicine and advocacy for organized efforts aimed at disease prevention became more fervent in the first decades of the 20th century, stimulating the growth of public health institutions, the growth of clinical preventive medicine as a professional discipline, and the implementation of screening programs [12, 13]. Local and state public health departments began to offer examinations. The broader cultural milieu was also conducive to the cause. Early in the century, the eugenics movement had considerable intellectual influence, and many arguments for periodic health examinations were replete with references to eugenic ideals [20]. A favorable ethos of technological optimism also began to take root, spurred by scientific innovations in medicine and other areas [13]. More medical technologies applicable to screening became available, adding to the content of periodic health examinations [13, 15].

War also furthered interest in the periodic health examination. Medical examinations were used in both World War I and World War II to assess the fitness of military recruits, and draft data showed a disconcertingly high percentage of physical defects and diseases among supposedly healthy young men [7, 8, 22, 34]. Exploiting the wartime cultural ethos, Fisk and others used draft data to promote periodic health examinations as a "national need" [20]. All this prompted the U.S. Army and Navy to require annual examination of all officers [8] and promoted interest in the periodic health examination in the medical profession and private industry [7].

Despite the evangelical advocacy of its pioneers, the periodic health examination met with apathy from the public in the early 20th century [10, 13, 35, 36]. Many practicing physicians also had little interest in the examination, citing lack of time and financial incentive. Other physicians were not convinced that the practice was effective [37, 38]. Acceptance was also impeded by historical factors. The Great Depression of the 1930s, World War I, and World War II diverted attention from the leisurely pursuit of individual health needs [13, 24]. In addition, access to physician care was lacking in the early 20th century and public perceptions of medical technology were such that people made relatively few visits to physicians in times of sickness, let alone health.

Renewed interest was generated after World War II with the development of "multiphasic screening"-the performance of multiple tests aimed at detecting unrecognized diseases or defects [39, 40]. The objective was mass screening that involved physicians only minimally and was done by using technology that could be applied economically and efficiently. The first endeavors were conducted in 1949 by the state health departments of California [40] and Massachusetts [41]. The practice subsequently spread and came to include more tests, usually aimed at screening for such diseases as tuberculosis, syphilis, and diabetes. Multiphasic screening promoted a trend toward more comprehensive periodic examinations and greater enthusiasm among physicians about screening endeavors, although many were wary of such efforts being performed outside of their own practices [36, 39, 42].

Administrative Concerns: Prepaid Health Care

Prepaid group-practice health care was a final important influence on the development of the periodic health examination through the mid-20th century. The most influential experience was that of the Kaiser Permanente Health Plan in the San Francisco area. This group began offering periodic health examinations to a small employer group in 1951, and the practice spread over the next several years. Approximately 25 000 screening examinations were performed annually for plan members in the San Francisco area by 1960, and about 50 000 were performed annually by 1970 [40].

The financial incentive structure of prepayment accounted for the success of the periodic health examination movement at Kaiser and created unique objectives that shaped its development. One objective was the satisfaction of an overwhelming patient demand for "health checkups." Sidney Garfield, cofounder of the Kaiser Permanente Health Plan, claimed that elimination of personally paid fees for medical care created an "insistent clamor for health checkups" that not only stimulated wider implementation of the periodic health examination but "threatened to overwhelm our entire medical department ... usurping available doctor time" [43]. Other prepaid group health plans in the United States experienced similar demand [39].

The goal of giving the public what it wanted led Kaiser to seek ways to maximize the efficiency of the examinations [44, 45]. They embraced multiphasic screening and sought to develop it further. In 1964, Morris Collen, director of the Medical Methods Research Department, developed an "automated multiphasic screening" procedure that incorporated computerized test equipment and data analysis [46]. The procedure consisted of a 3-hour comprehensive battery of tests that included historical questionnaires and many examinations and laboratory studies [47].

A broader objective was to triage patients within the system, to match their true needs with limited health care resources. The prepayment incentive structure created demand not just for periodic health examinations but for health care in general. The efficiency of the Kaiser system became compromised by what Garfield called an "uncertainty demand" of well and "worried well" health plan members who used "costly services from physicians through symptom complaints" because of insecurities about their true need for medical attention [43]. The periodic health examination was seen as a way to proactively regulate patient flow into the system, "to separate the entry mix into its three basic components-the well, the asymptomatic sick and the sick." By doing this, these groups could be matched with the appropriate level of care, thereby preempting the waste of true "sick-care service" by the uncertain well. Collen [44] argued that "it is more efficient for the providers of services to determine the patient's needs and to arrange appropriate care resources to meet those needs, than for the patient to arrange for the services he thinks he needs."

Kaiser physicians granted primacy to the maximization of efficiency over all other goals of the periodic health examination, including the early diagnosis and prevention of disease, which Garfield disclaimed as an anachronistic emphasis [43]. In the context of the new objective of patient triage, the content of the periodic examination became increasingly comprehensive. The "absent, vague or misleading symptoms of ‘uncertainty demand,’" Garfield argued, required a "comprehensive meticulous survey of body systems" [48]. The more information available to enable determination of a patient's true medical needs, the better.

The periodic health examination thus came to serve the purposes of satisfying patient demand for health care and improving the efficiency of the health care delivery system. These objectives led to the widespread implementation of the practice in such systems as Kaiser Permanente and to increasing comprehensiveness in the content of the examination.

The Age of Skepticism: The Modern Periodic Health Examination Movement

By the early 1960s, signs of broadening public acceptance of the periodic health examination had finally emerged. Opinion polls showed a growing popular belief in the value of the examination [49]. Utilization studies, such as the National Health Survey of 1960, showed that an increasing total number and percentage of visits to physicians were general checkups for adults [50]. The U.S. government began to formally examine multiphasic testing and sponsor research on the efficacy of the periodic health examination [39, 51, 52]. However, alongside growing acceptance by the lay public, the medical profession began to seriously question the value of the periodic health examination. Reflecting a growing emphasis in medicine from the 1960s, an increasing demand arose for evidence that periodic examinations could not only detect disease but could alter its course [24, 52]. This demand stimulated several empirical studies and efforts to reassess the effectiveness of the periodic examination.

Two major randomized, controlled trials were done to analyze the effectiveness of periodic health examinations in reducing mortality and morbidity rates. One, conducted by Collen and colleagues at Kaiser in 1964, enrolled approximately 10 000 adults and had follow-up and data analyses at 7 and 16 years [53-56]. The other, the South-East London Screening Study Group study [57], was done in London in 1967 and enrolled some 7000 adults with 9 years of follow-up. In both trials, the periodic health examination consisted of a comprehensive multiphasic examination and the major outcomes analyzed were health care utilization and overall mortality. Neither trial found significant differences in these outcomes between the study and control groups. Smaller trials produced similar results [58], as did many observational and retrospective studies in the 1960s [59-61]. These studies had methodologic problems that qualified their interpretation as negative or positive evidence [55, 57]. Nevertheless, no trial has produced convincing evidence for the effectiveness of the periodic health examination in decreasing morbidity or overall mortality.

Recognition of this lack of empirical evidence stimulated three major reassessments of the periodic health examination from the 1970s to the present. The first was an exhaustive literature review by Frame and Carlson in 1975 [62-64], with an updated review by Frame in 1986 [65-68]. These investigators selected 36 major medical conditions and evaluated 1) the accuracy of available screening tests for these conditions and 2) the effectiveness of early intervention in altering disease progression or mortality. They incorporated into the periodic examination only screening maneuvers that were proven to be accurate and effective.

The second major reassessment was done by the Canadian Task Force on the Periodic Health Examination. This multidisciplinary expert panel, commissioned by the Canadian government in 1976, adopted an overall approach similar to that used by Frame and Carlson. The Task Force viewed the periodic health examination as a collection of preventive services aimed at the early detection of specific diseases [2]. They began with an analysis of 78 conditions and examined the strength of available evidence for the effectiveness of screening measures in reducing disease-specific morbidity or mortality. They graded the empirical evidence according to its quality and graded their recommendations according to the grade of the supporting evidence. The group published its initial recommendations in 1979 [2] with subsequent updates [69-72].

The third major assessment was made by the United States Preventive Services Task Force, a panel formed in 1984 by the U.S. Department of Health and Human Services. This panel selected 60 target conditions representing leading causes of death and disability and evaluated specific preventive interventions by using explicit criteria and rules of evidence [73, 74]. The group published recommendations in 1989 and updated recommendations in 1996 [75, 76].

These three critical efforts were revolutionary in several ways. They reconceptualized the periodic health examination as an aggregate of discrete services representing current, state-of-the-art disease prevention rather than an irreducible, elemental practice. They discarded the idea of a single annual examination appropriate for everyone in favor of individualized examinations tailored to each person's unique risks for disease. They rejected many procedures that the periodic health examination had come to include; of those that were not rejected outright, many were done less often or were seriously questioned. The comprehensive history and the head-to-toe physical examination-the crux of the periodic health examination for so many years-could no longer be strongly recommended. Only certain parts of the examination, such as measurement of blood pressure, could be firmly endorsed for most adults, and only at qualified intervals.

After this empirical purging, a set of procedures remained that was radically minimalist compared with the long-promoted practice; the examination portion of the ideal periodic health examination was transformed from an exhaustive fact-finding survey to an expedient case-finding inspection. This version of the examination was advanced by various writers [77, 78] and endorsed by the American College of Physicians and the AMA [4, 31]. The transformation was sufficiently radical to nullify the necessity of an en bloc periodic health examination; the Canadian and U.S. panels both affirmed that the examination's components could ideally be performed as case-finding maneuvers during visits for illness [2, 71, 75, 76].

The authors of all three reassessments were careful to affirm that a lack of empirical data did not constitute evidence of a measure's ineffectiveness and that their recommendations about content represented the minimum that should be done rather than the maximum. They also highlighted the incorporation of preventive services other than screening, such as counseling, immunization, and chemoprophylaxis. Nevertheless, the aim and effect of the reassessments were to give clinicians serious pause in advocating many accepted procedures of the periodic health examination. Because of the great disparity between expert recommendations and conventional practice, many clinicians felt obligated to rethink-and often to disregard and "unsell"-long-valued practices [79].

These changes represented a fundamental shift in the main objectives of the periodic examination. Reflecting the emphasis of modern evidence-based medicine, the three studies emphasized reduction of disease-specific morbidity and mortality as the principal objective of the periodic health examination, the criterion by which its effectiveness should be judged [80, 81]. None of the other objectives (such as building a patient database or developing the physician-patient relationship) that had formerly justified the periodic examination were granted evaluative weight [82]. All three groups began by defining the periodic examination as a procedure primarily for the early detection of specific diseases and arrived at similarly minimalist conclusions. More than a mere advance in analytic standards, the modern skeptical demand for empirical evidence implied a change in objectives that diminished the content of the periodic examination and engendered controversy among its practitioners.

Conclusions

Through its history, the periodic health examination has evolved from a comprehensive fact-finding survey to a selective set of case-finding maneuvers and preventive measures. It has gone from being ignored to being demanded by the general public and from being resisted to being recommended and redefined by the medical profession. Its content, legitimacy, and effectiveness have been judged in terms of objectives that have changed considerably. Although almost all of its advocates have made some reference to the goal of early disease detection and the reduction of morbidity and mortality, other objectives have been equally important: scientific knowledge, economic savings, professional empowerment, the physician-patient relationship, data collection, satisfaction of patient demand, and administrative efficiency. The objectives that have been emphasized reflect the concerns of the strongest advocates of the periodic health examination at various times.

Because the development of the periodic health examination has been driven by changes in its underlying objectives, it is difficult to laud the contemporary ideal of this examination as an evolutionary advance. Undoubtedly, analytic methods have been refined since the first empirical studies of the periodic examination were done, and the modern demand for greater methodologic rigor and certainty of effectiveness represents a positive advance. But the underlying objectives that have defined the periodic examination cannot be construed as advancing in the same way; they have primarily reflected ongoing shifts in deeper cultural and ethical values. In the context of the changing cultural milieu in which the periodic health examination has been proffered, concern has shifted from the costs of disease-whether to patient, insurer, employer, or society-to the costs of medical intervention. An optimistic ethical viewpoint emphasizing the potential benefits of medical technologies has been replaced by a skeptical posture emphasizing potential harms. A favorable outlook toward the expansive application of medical interventions has been supplanted by a cautious stance that eschews the encroachment of the medical profession on the lives of healthy persons [2].

The objectives of the periodic health examination have continually evolved in the context of these shifting concerns. From a historical perspective, it is therefore not clear that the contemporary aim of disease-specific morbidity and mortality reduction is more legitimate than any other objectives that have defined the periodic health examination in the past. In fact, these other objectives deserve continual reevaluation and may have great relevance in the current health care environment. For example, the fostering of physician-patient relationships may be a legitimate goal for the periodic health examination [79-81]. If so, such items as the head-to-toe physical examination may be valuable in allowing the laying-on of hands-an aspect of physical examination that has great potential importance in the physician-patient relationship [83-85]. Other legitimate goals of the periodic health examination may be to improve patient and physician satisfaction or the quality and efficiency of care; to achieve these goals, fact-finding might be as important as case-finding. These objectives seem especially relevant in the growing managed care environment, in which regular check-ups are often promoted to patients for marketing purposes and in which asymptomatic plan members are increasingly asked during times of health to establish relationships with primary care physicians upon whom they must depend for access to further care. Paradoxically, however, although periodic health examinations might improve the overall efficiency of care (as the early leaders at Kaiser Permanente believed), it is conceivable that the productivity demands of managed care might not allow sufficient time to conduct such examinations adequately.

Alternative goals such as these are difficult to operationalize, and evidence for the effectiveness of the periodic health examination in achieving them is lacking. Yet, their importance fuels at least some objections to the contemporary ideals that define the periodic examination solely as a screening exercise [79]. Limited work has explored the examination's effectiveness in achieving objectives other than morbidity and mortality reduction, such as case-finding [86, 87] and reduction of health care utilization and costs [88], but more work exploring other potentially important objectives is needed. Meanwhile, the dilemma faced by present-day clinicians (among whom substantial practice variation exists [89]) is not only to decide whether available evidence supports particular aspects of the periodic health examination but to choose which objectives of the examination are pertinent. I have tried to show that these choices are determined by deeper concerns and that critical evaluation of the periodic health examination requires an understanding of the historical factors that have shaped it.