Medical Statistics of the United States Army, Calendar Year 1954
APPENDIX
Sources, Definitions, and Methodology
SOURCES
Primary Source
Individual medical records constitute for Army personnel the source of all data relative to admissions, dispositions, and days lost from duty, except for a few instances where other sources are specifically cited. These records are submitted monthly by each Army medical treatment facility, worldwide, for all dispositions of personnel treated on an excused-from-duty basis, plus certain other cases ?carded for record only.? (See definition of ?CRO cases? on p. 132.) The records are submitted on the Medical Report Card (DA Form 8-24), the Field Medical Card (DA Form 8-26), or the Emergency Medical Tag (DA Form 8-27). The individual medical record summarizes the salient facts of the case, including the date and place of initial admission and each transfer to another medical treatment facility, the conditions treated, the circumstances relating to injuries, the surgical operations performed, the length of stay in hospital, quarters, on leave, etc., and the type of final disposition. In addition to the reports submitted for completed cases, an interim report called a ?Remaining Card? is made on cases treated during the year but not disposed of by a particular subsequent date. This makes it possible to complete the experience for the particular year and so to compute rates, etc.
Summary Report Sources
The Morbidity Report (DD Form 442) is a summary submitted by each medical treatment facility for the 4 or 5 weeks ending with the last Wednesday of each month, and showing the number of admissions, dispositions and cases remaining, separately for Army, Navy, Air Force, and all other personnel. It includes a distribution of cases (including ?CRO? cases) by diagnostic class and selected diagnoses, and reports the average number of persons regularly provided their primary (dispensary type) medical care by the facility. Data from this report may be somewhat incomplete for deaths, since ?CRO? deaths (cases not admitted to a medical treatment facility) are not always properly reported. Other inaccuracies may sometimes occur as a result of failure, to record changes in initial diagnoses or certain addi?tional conditions arising after admission. However, the report is valuable as a preliminary summary of morbidity data, and its 100 percent coverage is often useful as a supplement to final data tabulated from individual medical records on a sampling basis.
The Beds and Patients Report (DD Form 443) furnishes for each Army hospital and infirmary a monthly (report month) census of patients, by type, itemizes the flow of patients, and indicates the available bed capacity and the extent of its utilization.
The Outpatient Report (DD Form 444) is prepared for each 4- or 5-week report-month to provide data on medical care furnished to outpatients, that is, to patients treated without being excused from duty. The report arranged, by category of personnel, includes data on outpatient visits and treatments and the frequency of various types of physical examinations and immunizations.
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The Dental Service Report (DD Form 477) is prepared monthly by each Army installation or unit which provides its own dental service. The report shows, by type of personnel, dental operations and treatments; examinations completed; personnel data, etc.
The Report of Veterinary Meat and Dairy Hygiene Inspection (DD Form 8-134) is prepared monthly by all Army installations or units with meat and dairy inspection activities. Information on Army-owned animals, including admissions, days lost, and deaths, is derived from the Veterinary Report of Sick and Wounded Animals (DD Form 8-129).
The Summary of Registrant Examinations for Induction (DA Form 316) is prepared by each induction station, with a separate report for each state from which registrants are customarily processed, and is submitted monthly to the Office of The Surgeon General. The report deals with the following: results of preinduction examinations; results of inspections and complete examinations of registrants forwarded for induction; number inducted into each service, and the number of inductees having venereal disease; registrants found acceptable, distributed by physical category and mental group; registrants who failed the mental test but were medically acceptable, distributed by physical category and mental subgroup; and results of examination for certain groups of registrants, such as conscientious objectors.
Sources of data on Army Medical Service commissioned personnel are cited on source tables 24, 25, and 26.
DEFINITIONS
Admissions, for military personnel on active duty, refers to the number of individuals who entered a hospital, infirmary, or dispensary for treatment or observation as ?new cases? and who were not returned to duty status before midnight of the same day. (Note that this includes all deaths after admission, even though occurring on the day of admission.) The term includes cases treated in quarters and personnel admitted to Army medical treatment facilities (e. g., a case admitted to a nonmilitary hospital while on leave). Cases carded for record only (see definition of ?CRO cases? on p. 132) are omitted from admission counts and rates in 1954; the effect of this change from the procedure of previous years is discussed in the text. For other than military personnel on active duty, ?admissions? refers to the number of individuals admitted as inpatients at Army medical treatment facilities.
Incidence for a given diagnosis refers to the total number of new cases reported for the condition, including secondary diagnoses as well as causes of admission. CRO cases are excluded from the 1954 incidence data for Army personnel on active duty, and the effect of this exclusion is discussed at appropriate points in the text.
Battle casualties, except for the 2 killed in action (KIA) cases on Quemoy Island, are limited to those casualties arising as new cases during the Korean Conflict, and whose initial admission extended into 1954. Note that of the 1,033 cases extending into 1954, only 52 were still in hospital at the end of the year. Data for these cases are presented to supplement other data on noneffective days and disability separations. A later report will include final data on all 1950-1953 battle casualties.
New cases refers to cases not previously recorded on an individual medical record by any military medical treatment facility. The term includes cases treated for conditions existing prior to service (EPTS), but includes only the first admission after entry into military service; all subsequent admissions are cases previously recorded or readmissions. However, over a period of time more than one new case of a given diagnosis may be recorded for the same individual, provided the second and subsequent episodes are independent and not continuations of the previous episode Thus, repeated but separate attacks of such acute conditions as common cold, pneumonia, dysentery, etc., are all regarded as new cases. Similarly, new injuries or new distinct cases of communicable disease are classified as new
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even though the individual may have previously incurred a similar injury or sustained a separate attack of the same acute disease.
CRO cases are cases carded for record only as distinguished from cases recorded (or ?carded?) because they are admissions. An individual medical record is prepared for each death, disability separation, battle casualty, and each new case of venereal disease and of nongonococcic urethritis; if such cases are not admissions, they are carded for record only. A CRO individual medical record is also prepared in the case of certain administrative separations (inaptitude, unsuitability, pregnancy, etc.) that have a medical basis. In addition, a CRO individual medical record may be prepared for outpatients having a condition that, in the opinion of the attending officer, might result in a later claim upon the Government. CRO cases are included in tabulations of deaths and disability separations, but are excluded from admissions and from Army incidence data. See text for comparability of admission and incidence rates for 1954 and previous years.
Average strength. Rates are based on average strengths provided each report month on DD Form 442 (Morbidity Report). The strength reported is the average daily number of persons entitled to receive primary (dispensary type) medical care from the medical facility making the report. The average strengths for different installations are combined to obtain average strengths by broad areas for a given report month. The average strength for the year is computed by weighting appropriately and combining the average strength for each report month. To obtain certain breakdowns of the average strength, such as by age, length of service, etc., the average strengths derived from DD Form 442 are distributed in the proportions shown by data available from the Office of The Adjutant General.
Rates of admission, incidence, and separation are generally presented in this report in terms of number per 1,000 average strength per year. Death rates, because of their lowness for most categories, are presented as number per 100,000 average strength per year. The rate is computed by dividing the number of admissions (or deaths, separations, etc.) by the average strength for the period covered. When annual rates are computed for periods of less than one year, the experience during the observed portion of the year is multiplied by an appropriate factor in order to indicate what the annual experience would have been had the same relative level prevailed throughout the rest of the year.
Days lost from duty because of illness or injury represent the difference between the calendar day of admission and the calendar day of final disposition, that is, disposition other than by transfer to another military hospital. Included are days in hospitals, infirmaries, quarters, dispensaries, and other locations while the patient is under the medical supervision of an Army medical treatment facility, days in transit, and days on leave or AWOL (absent without leave), with the provision that after 10 consecutive days of AWOL, the case will be closed. Total days lost are presented in two ways: (1) average duration and (2) the noneffective rate.
Average duration, as presented in this report, is based on dispositions during 1954, including cases admitted in prior years, and excluding CRO cases The days include the total time that elapsed from the date of admission to the date of disposition. For deaths, disability separations, and administrative separations, the average duration represents time lost on the final admission; for other disposition groups, and for all dispositions combined, days lost by the relatively small numbers of readmissions (about 1 percent, for all disease) have been considered as continuations of the original admission. Averages for deaths and disability separations are presented by underlying cause of death or by residual disability; all other average durations are presented by the diagnosis which was the cause of admission. Average durations for single diagnosis cases are presented in order to assess the effect of secondary diagnoses. Average durations for military personnel are not comparable to civilian hospital ?days per admission.?
Noneffective rate. The noneffective rate per 1,000 average strength is the average number of persons per day who are in an excused-from-duty status because of illness or injury. This is a rate of the prevalence type, and is computed by accumulating the total days lost during the year (by cases carried over from the previous year and by readmissions,
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as well as by new cases during the current year) and dividing by 365 times the average strength (in thousands).
Rank. The category ?officers? includes warrant officers as well as commissioned officers. Male and female personnel are included in ?officers? and in ?enlisted? personnel.
Race. The category ?white? includes all cases not specifically stated to be Negro. Of the total number of individual medical records received, about 0.5 percent were for ?other races? (other than Caucasian or Negroid) and 0.25 percent were classified as of unknown race. Including both of these categories in the group characterized as white has no appreciable effect on the resultant rates.
EPTS is an abbreviation for ?existing prior to service.? The EPTS condition is considered to be incurred ?not in line of duty? unless qualified as ?EPTS, aggravated by service.?
METHODOLOGY
Individual medical records are received and processed by the Medical Statistics Division of the Office of The Surgeon General. Because of the large volume of these records, it is feasible to process only a sample of the total records received. This section of the report describes briefly the method of sampling, and its effects upon the data presented.
Processing individual medical records. All of the individual medical records received are reviewed for conformance with reporting requirements. For sampling purposes, records for Army personnel are grouped into three broad classifications:
1. Special cases. This group includes all deaths; all disability separations; all battle casualties; all cases recovered from enemy control; all cases evacuated to the continental United States in a patient status; and certain nondisability separations from service, such as separations for inaptitude and separations for nonmedical reasons.
2. Other cases, 20 percent sample.
3. Other cases, residual 80 percent which are not used in tabulations.
The last two categories of cases include all cases that do not fall into any of the ?special? categories. The 20 percent sample is selected on the basis of the units digit of the service number, which identifies each individual in the Army. Since service numbers ending in any particular digit should occur with about the same frequency as those ending in any other, the service numbers ending in any two specific digits should constitute a 20 percent sample of all Army cases.
All of the records in groups 1 and 2 are translated into codes which are written on "transcription slips? and then punched into tabulating cards. In general, these codes cover the following information:
Identification of patient (service number).
Classification of patient, (rank, sex, race, age, length of service, branch of service, etc.).
Admission data (place and date).
Disposition data (place or type of medical treatment facility, date, nature of disposition made of the case).
Days lost from duty (total in each calendar year, total for completed case, days overseas, bed-occupancy days, days on leave, etc., and days in quarters).
All diagnoses reported, together with related information (whether ?new? or ?previously recorded,? the anatomical location, the principal surgical operation for each diagnosis, the causative agent of injuries, and the principal residual condition or ?final result,? if any). Since the punch card form provides space to record only two diagnoses and their related fields, any additional diagnoses are punched into ?trailer cards,? using as many as necessary; the punching in trailer cards for a given case is identical with the ?principal card? for the case except for the diagnostic information. The code used is based on the International Statistical Classification Diseases, Injuries, and Causes of Death of 1948 as adapted for use by the Army,
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Navy, and Air Force in SR 40-1025-1, ?Joint Armed Forces Statistical Classification and Basic Diagnostic Nomenclature of Diseases and Injuries.? The principal modification is in the coding of neoplasms and traumatisms, which are classified in much greater diagnostic detail, with the anatomical location involved coded as a separate item.
Data which pertain to battle casualties only (or to deaths only, or to disability separations only), have been tabulated from auxiliary files containing data on a 100 percent (no sampling) basis. All other data (admissions, incidence, noneffective days, average days per case, etc.) are tabulated from the 20 percent file of nonbattle conditions. Note that these 20 percent tabulations include the 20 percent portion of deaths, separations, etc.
Confidence limits. The discussion of confidence limits which follows applies only to data derived from the 20 percent sample used for most of the tabulations of individual medical records. However, even with data that have not been sampled (e. g., deaths or separations), there is need for caution in using rates based on a small number of cases or a small segment of the Army. For example, the death rates per 100,000 average strength in the 20-24 year age group are much more reliable than the rates for, say, the 40-44 year age group. The rate for the younger age group represents the experience of an average strength of several hundred thousand, while for the 40-44 year group, the rate is an estimate of what the rate would have been if the average strength had been as large as 100,000. Note that when the average strength is considerably less than 100,000 the rate increases rather substantially for each death. When the rate is based on a fairly large number of deaths, variations from year to year are relatively small in proportion to the rate itself, but when the rate is based on, say, one or two deaths, any change is bound to be large in relation to the rate itself.
Card counts from the 20 percent sample have been multiplied by 5 in order to show the total number of cards that presumably would have been obtained if all records had been processed. Consequently, all frequencies based solely on the 20 percent sample are multiples of 5. These figures may be somewhat higher or lower than the true figure, and this ?sampling error? exists whether the data are presented as frequencies or are converted into rates. Thus it is useful to know how far the ?true value? might differ from the estimate based on the 20 percent sample, and with what degree of confidence one could expect the true value to be within specified limits.
?Confidence limits? indicate the range within which the ?true value? (derived from 100 percent of the records) can be expected to fall with a specified degree of assurance. The 95 percent and 99 percent degrees of confidence are two of the moat commonly used. Using the 95 percent confidence limits, one may say that the chances are 95 out of 100 that the true value lies between the limits shown. Likewise, there is only one chance in 100 that the true value lies outside the 99 percent confidence limits.
Data from the 20 percent sample are not intended to show exact numbers of cases. Very low frequencies of zero, 5, 10, 15, etc., based on- the 20 percent sample, obviously have a higher percentage of error than large frequencies. For certain diseases of very low incidence, the Morbidity Report is a useful source for obtaining comparative data, and this source has been utilized in the discussion of these diseases. Certain other data shown in the tables may be based on very low frequencies because the condition has been subdivided or cross-classified by other variables. Whenever low frequencies occur, they should not be read literally, but should be evaluated in terms of the sampling error they may contain. Table LXVII shows the limits within which the true frequency may be expected to lie, when frequencies of 100 or less are based on a 20 percent sample.
The amount of sampling error in rates based on the 20 percent sample depends on (1) the size of the rate itself, and (2) the size of the population or average strength from which the sample was drawn.
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Table LXVIII presents the standard error for specified rates and average strengths, based on the formula for the standard error of a proportion. Values for intermediate rates and strengths not shown in the table may be approximated by interpolation. From these standard error values, approximate 95 percent confidence limits may be computed by adding and subtracting two (more precisely, 1.96) standard errors to the rate based on the 20 percent sample. The approximately 99 percent confidence limits may be computed by adding and subtracting 2.58 standard errors to the rate computed from the 20 percent sample. For example, if the rate was 10 per 1,000 average strength, based on the 20 percent sample of 250,000 average strength, the chances are 95 out of 100 that the true rate lies between 9.12 per 1,000 and 10.88 per 1,000 average strength; or, the chances are 99 out of 100 that the true rate lies between 8.86 and 11.14 per 1,000 average strength.
TABLE LXVII.?APPROXIMATE CONFIDENCE LIMITS FOR FREQUENCIES BASED ON A 20 PERCENT SAMPLE
| Number of cases in 20 percent sample | Frequency shown in tables | Probable range of number in total population | Number of cases in 20 percent sample | Frequency shown in tables | Probable range of number in total population | ||
| 95 percent confidence limits | 99 percent confidence limits | 95 percent confidence limits | 99 percent confidence limits | ||||
| 0 | - | 0-17 | 0-24 | 11 | 55 | 30-94 | 24-108 |
| 1 | 5 | 1-26 | 1-35 | 12 | 60 | 33-100 | 28-115 |
| 2 | 10 | 2-34 | 2-44 | 13 | 65 | 37-106 | 31-121 |
| 3 | 15 | 3-41 | 3-51 | 14 | 70 | 41-112 | 35-127 |
| 4 | 20 | 6-49 | 4-59 | 15 | 75 | 45-118 | 38-133 |
| 5 | 25 | 9-55 | 6-66 | 16 | 80 | 49-124 | 41-139 |
| 6 | 30 | 12-62 | 9-74 | 17 | 85 | 52-130 | 45-145 |
| 7 | 35 | 15-69 | 12-81 | 18 | 90 | 56-136 | 49-151 |
| 8 | 40 | 19-75 | 15-88 | 19 | 95 | 60-141 | 52-157 |
| 9 | 45 | 22-82 | 18-95 | 20 | 100 | 64-146 | 56-163 |
| 10 | 50 | 26-88 | 21-101 | ||||
It should be noted that in table LXVIII the standard errors of the rates are approximate values only. Because the sample is from a finite population (total Army, a specific geographic area, sex, race, rank, etc.), a finite population correction might be applied to the listed value of the standard error. Since the sampling fraction is 20 percent, the values corrected for finite sampling would be approximately 0.9 times the values shown in the table. Thus the uncorrected values shown overestimate slightly the standard error. It should also be noted that if the confidence limits are computed as indicated in the footnote to table LXVIII, the limits may not be reliable for the smaller rates shown when based on the smaller strengths. This is due to the fact that the normal approximation to the binomial distribution is being used to obtain confidence limits (although, in fact, the true distribution is hypergeometric). For very small numbers (and therefore for very small rates), confidence limits can be obtained from table LXVII, which is based on accurate computations of confidence limits for the hypergeometric distribution.
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TABLE LXVIII.?APPROXIMATE SAMPLING ERROR IN RATES BASED ON A 20 PERCENT SAMPLE
| Rate per 1,000 average strength (as shown in tables)a | Standard error of rate per 1,000 average strength assuming various average strengthsa | ||||||||
| 1,500,000 | 1,000,000 | 750,000 | 500,000 | 250,000 | 100,000 | 50,000 | 25,000 | 10,000 | |
| 1 | 0.06 | 0.07 | 0.08 | 0.10 | 0.14 | 0.22 | 0.32 | 0.45 | 0.71 |
| 2 | 0.08 | .10 | .12 | .14 | .20 | .32 | .45 | .63 | 1.00 |
| 3 | .10 | .12 | .14 | .17 | .24 | .39 | .55 | .77 | 1.22 |
| 4 | .12 | .14 | .16 | .20 | .28 | .45 | .63 | .89 | 1.41 |
| 5 | .13 | .16 | .18 | .22 | .32 | .50 | .71 | 1.00 | 1.58 |
| 6 | .14 | .17 | .20 | .24 | .35 | .55 | .77 | 1.09 | 1.73 |
| 7 | .15 | .19 | .22 | .26 | .37 | .59 | .83 | 1.18 | 1.86 |
| 8 | .16 | .20 | .23 | .28 | .40 | .63 | .89 | 1.26 | 1.99 |
| 9 | .17 | .21 | .24 | .30 | .42 | .67 | .94 | 1.34 | 2.11 |
| 10 | .18 | .22 | .26 | .31 | .44 | .70 | 1.00 | 1.41 | 2.23 |
| 20 | .26 | .31 | .36 | .44 | .63 | .99 | 1.40 | 1.98 | 3.13 |
| 30 | .31 | .38 | .44 | .54 | .76 | 1.21 | 1.71 | 2.41 | 3.82 |
| 40 | .36 | .44 | .51 | .62 | .88 | 1.39 | 1.96 | 2.77 | 4.38 |
| 50 | .40 | .49 | .56 | .69 | .97 | 1.54 | 2.18 | 3.08 | 4.87 |
| 60 | .43 | .53 | .61 | .75 | 1.06 | 1.68 | 2.37 | 3.36 | 5.31 |
| 70 | .47 | .57 | .66 | .81 | 1.14 | 1.80 | 2.55 | 3.61 | 5.71 |
| 80 | .50 | .61 | .70 | .86 | 1.21 | 1.92 | 2.71 | 3.84 | 6.07 |
| 90 | .52 | .64 | .74 | .90 | 1.28 | 2.02 | 2.86 | 4.05 | 6.40 |
| 100 | .55 | .67 | .77 | .95 | 1.34 | 2.12 | 3.00 | 4.24 | 6.71 |
| 150 | .65 | .80 | .92 | 1.13 | 1.60 | 2.52 | 3.57 | 5.05 | 7.98 |
| 200 | .73 | .89 | 1.03 | 1.26 | 1.79 | 2.83 | 4.00 | 5.66 | 8.94 |
| 250 | .79 | .97 | 1.12 | 1.37 | 1.94 | 3.06 | 4.33 | 6.12 | 9.68 |
| 300 | .84 | 1.02 | 1.18 | 1.45 | 2.05 | 3.24 | 4.58 | 6.48 | 10.25 |
| 350 | .87 | 1.07 | 1.23 | 1.51 | 2.13 | 3.37 | 4.77 | 6.75 | 10.67 |
| 400 | .89 | 1.09 | 1.26 | 1.55 | 2.19 | 3.46 | 4.90 | 6.93 | 10.95 |
| 450 | .91 | 1.11 | 1.28 | 1.57 | 2.22 | 3.52 | 4.97 | 7.04 | 11.12 |
| 500 | .91 | 1.12 | 1.29 | 1.58 | 2.24 | 3.54 | 5.00 | 7.07 | 11.18 |
aBased on the formula for the standard error (S. E.) of a proportion, S. E. =√p(1-p)/n where p is the proportion observed in the sample (and is thus 1/1,000 times the rate) and n is the size of the sample. Sample rate ?1.96 S. E. includes true rate with 95 percent assurance. Sample rate ?2.58 S. E. includes true rate with 99 percent assurance. Not corrected for finite population or for error in normal approximation; see text.
