NAPA Bulletin 13 Gordon, Claire C. & Thomas M, Greiner – Biocultural Influences in the Analysis of Secular Trends. (Race, Ethnicity, And Human Engineering)

8/21/2019 NAPA Bulletin 13 Gordon, Claire C. & Thomas M, Greiner – Biocultural Influences in the Analysis of Secular Trends. …

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Biocultural Influences in the Analysis of Secular Trends

Claire C. Gordon and Thomas M. Greiner

In a human-engineering setting, anthropometric data col lection and

statistical analyses focus on target populations—the aggregates of persons

ho ill utili!e a particular materiel system or design. Because designs

may "e in use for se#eral decades after their introduction, secular trends in

the anthropometric distri"utions of target populations are of great concern

to the human-factors engineer. These target populations are formed

primarily through cultural processes that sample indi#iduals from $parent$

"iological populations. %nli&e many "iological populations, temporal

analyses of target populations lac& an a priori "asis for assuming

"iocultural continuity. To de#elop applied secular-trend models, it is thus

necessary to or& around this limitation. 'ne approach to this process ill

"e illustrated "y constructing secular-trend models for the target population

of the %.S. Army.

Secular-Trends Models

Secular trends are fre(uently #ieed as "iological responses to a

changing en#ironment. Impro#ed socioeconomic status, for e)ample, is

generally associated ith "etter health care and nutrition, and greater at-tainment of genetic potential for groth. *erein lies the more traditional

realm of secular-trends analysis. 'nly "iological populations undergo

secular change as a direct response to a changing en#ironment. *oe#er,

secular changes in "iological parent populations can influence the anthro-

pometric distri"utions of engineering target populations. Thus, secular

trends o"ser#ed in the army ill "e due, in part, to secular trends in the

%.S. population.

Target populations are "uilt through the actions of culturally determinedsampling processes, or $cultural filters,$ hich determine population

mem"ership. Thus, secular trends of target populations may "e modeled as

the interaction of cultural and "iological processes +see igure that

change parent populations and influence their relati#e contri"ution to the

target population. Army cultural filters inc lude the effects of recruiting

strategies, entrance re(uirements, and #arious societal opinions regarding

the merits of military ser#ice. Cultural filters, hoe#er, can also change o#er

time. This change might "e e)pressed as a change in recruiting strategies

//


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0A1A B%223TI0 4 /4

Time 1 Time 2

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t

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677

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Grei

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. In

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targe

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lar-

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plica

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that

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. The

ident

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t

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of

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, this

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ectly

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/; :AC3, 3T*0ICIT@, A0 *%MA0 30GI033:I0G

Table 1Filters Influencing Migration of Ciilians into t!e Army

. Anthropometric :e(uirements

/. ifferential :ecruitinga.Gender ".:acial5ethnic groupc.Age

4. Secondary actorsa.3conomic status and incenti#es".3ducational re(uirements for military 9o"sc.3ntrance e)am scores

change o#er time. A com"ination of o#ert military recruiting strategies and

co#ert cultural opinions can effect change through differential selection "y

se), racial5ethnic group, and age. The effects of this type of selection can

"e addressed in secular-trend studies "y di#iding the sur#ey data into ap-

propriate demographic su"groups and modeling each separately. Changes

in selection criteria for se), race5ethnicity, and age can then "e in-

corporated in secular-trend models "y #ieing the target population as acomposite of these parts and utili!ing eighted estimates.

A third type of cultural filter might "e selection on a cultural factor op-

erating ithin demographic su"groups that correlates ith, "ut is not di-

rectly related to, anthropometric dimensions. 'ne e)ample of this might

"e preferential selection "y le#el of education. 3ducation le#els are often

related to socioeconomic status, hich in turn is associated ith a host of

"iological #aria"les that influence anthropometric distri"utions +legal et

al. 677a, 667"8 Garn et al. 68 *arlan et al. 677. The strength of these types of associations, hoe#er, #ares across cultural groups

+legal et al. 677a, 677"8 Meredith 6>. In any case, educational data

are not routinely a#aila"le for army anthropometric sur#ey su"9ects. Thus,

only general trends of educational selection can "e discussed. 'ther

cultural criteria might also "e at or& that ha#e no measura"le surrogate.

The action of the cultural filter in this fashion can therefore not "e

controlled or anticipated, and this constitutes a primary limitation in all

applied secular-trend models.

Analytical Methods

3ach sur#ey represents a snapshot of anthropometric #ariation ithin

the army population +see Ta"le /. To lin& these data sets, indi#iduals are

grouped into cohorts that represent fi#e-year "irth inter#als. olloing pro-

cedures outlined "y Greiner and Gordon +66/, the mean #alue for each

"ody dimension is calculated for each cohort. These #alues are then ad-


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Table 2

Birth Year Cohorts and Subjects' Ages by Survey Year

Cohort

Subjects' Ages When Measured

Birth Years1946 1966 1977 19

1 1!"9 !7# 19$"94 !#"!6% 19!"99 47"!14 19$$"$4 4#"46 6#! 19$!"$9 %7"41 !7"616 191$"14 %#"%6 !#"!67 191!"19 #7"%1 47"!1 ! 19#$"#4 ##"#6 4#"46 !%"!79 19#!"#9 #1 %7"41 4"!# !91$ 19%$"%4 %#"%6 4%"47 !4"!11 19%!"%9 #7"%1 %"4# 49"!%1# 194$"44 ##"#6 %%"%7 44"41% 194!"49 17"#1 #"%# %9"4%14 19!$"!4 16 #%"#7 %4"%1! 19!!"!9 1"## #9"%%16 196$"64 17 #4"#

17 196!"69 19"#%1 197$"74 1

justed &or age"reated change and sub(itted to regression anaysis) *o ac"

co((odate very arge di&&erences in sa(+e si,es- each cohort's (ean

vaue can be .eighted by cohort si,e in the statistica anayses)

*hese variate regressions +roduce the &oo.ing generic e/uation0

AA 2 a C+ b

3n this inear e/uation- b is the y"interce+t constant and a is the so+e o&

the ine) Because this e/uation describes the reationshi+ bet.een cohort

(C) and an age"adjusted anthro+o(etric di(ension AA5- the ter( a isthe rate o& secuar change +er &ive"year +eriod)

Whie a ongitudina +ers+ective &or secuar"trend anayses can be ob"

tained by ining the data &ro( t.o or (ore anthro+o(etric surveys- their

(easuring techni/ues (ust be care&uy scrutini,ed) ny di(ensions

(easured through stricty co(+arabe techni/ues can +rovide data &or the

anaysis) 3n addition- the de&inition o& +o+uation subgrou+s (ust be co("

+arabe) 8urther(ore- a 3 reevant birth years (ust be broady re+resented

in the avaiabe data) When these restrictions are a++ied to )S) Ar(y data

bases- their co(bination +er(its a (ae anaysis co(+rised o& &our ra"

cia:ethnic grou+s .hites- bacs- ;is+anics- and Asian:?*3= 1% #!


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#6 @AC?- ?*;=3C3*Y- A= ;MA= ?=3=??@3=

igure /. *ead "readth +mm "y "irth-year cohort.

and a female analysis of only to racial5ethnic groups +hites and "lac&s.Dhen insufficient data limit modeling to only some segments of the target

population, this clearly induces some limitations to the application of re-

sults. *oe#er, in this case "ecause hites and "lac&s together comprise

64.; percent of the females in the army +Gordon et al. 676, this limitation

may not "e too serious.

Temporal Sta"ility of Secular-Trends Models

The cru) of secular-trend analysis lies ith the construction of relia"le

and temporally sta"le models for each of the identified target population

su"groups. An important aspect of this is the re#ie and specification of

any temporally unsta"le cultural influences. A parallel e)amination of esti-

mated secular trends in %.S. Army males and females pro#ides an

e)ample of the differential operation of cultural filters and their relati#e

influence on model relia"ility.

Three ma9or sur#eys of army omen are a#aila"le to "uild seculartrend

models. *oe#er, hen these data are plotted against "irth-year cohort,

there is a consistent separation of the 6;> data set, most dramatically seen

in igure /E a scatterplot of head "readth #ersus "irth-year cohort. The

special nature of se#eral factors operating on the 6;> army omen may

e)plain this separation. irst, the "ul& of these omen e)perienced their

groth years during the Great epression of the 64


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Table Recent Milestones for U.S. Army "omen

6> 1u"lic 2a 6 data set represent the forma-

tion of the Domen?s Army Corps in response to the national emergency of

Dorld Dar II +DDII. As an e#ent, DDII represents a comple), uni(ue, and

discontinuous cultural filter hose direct and indirect influences on anthro-

pometric #alues are difficult to discern. There are insufficient data to $cor-rect$ for the uni(ue influence that DDII had on army omen?s anthropomet-

ric distri"utions. Therefore, the only alternati#e is to ac&noledge that the

6;> sur#ey data represent a separate target population that cannot, at this

time, "e lin&ed to the later sur#eys in a larger trend model. 'ngoing re-

search in this area ill attempt to identify social and demographic differ-

ences "eteen the DDII-era Domen?s Army Corps, their ci#ilian counter-

parts, and their military $descendants.$

Dhi le analysis of the remaining to data sets +6 and 677 resultsin more sta"le secular-trend models, their lac& of time depth may limit

model relia"ility. The 6 and 677 sur#eys o#erlap for all "ut to "irth-

year cohorts. Therefore, these data do not pro#ide long-term information

on ho cultural processes might "e affecting the population. 0e#ertheless,

changes in the cultural filters affecting army omen might "e associated

ith e#ents "eteen 6> and 67 +see Ta"le 4.

In effect, "eteen 6> and 67, there as a "roadening of the cul-

tural selection criteria that influenced omen?s participation in the army.These changes may ha#e indirectly influenced anthropometric dimensions

e#en though no specific change in anthropometric selection criteria oc-

curred. It is difficult to del ineate indirect cause and effect relationships "e-

teen cultural actions and anthropometric trend. *oe#er, if it could "e

shon that ne cultural filters "ring a"out a shift in the socioeconomic ori-

gins of omen recruits, then inclusion of socioeconomic le#el, or some

pro)y for it, may "e needed to enhance model relia"ility. 'ne possi"le

measure that might "e used is the association of socioeconomic le#el ithle#els of education. uring the period of 6> to 67, for e)ample, accept-

0A1A B%223TI0 4 /


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28 RACE, ETHNICITY, AND HUMAN ENGINEERING

a"le le#els of education ere "roadened and entrance le#els ere loered

for omen recruits. *oe#er, these changes did not palpa"ly affect the di

stri"ution of omen?s education le#els +Soldier Support Center 67/8 %.S.

Army Military 1ersonnel Center 6. Therefore, education +e#en if it erea useful pro)y for socioeconomic le#el may not "e useful in e)plaining the

secular trends of army omen.

Because the original 6;> sur#ey data for men are not a#aila"le, the

6>> and 677 sur#eys of army men ha#e "een used to "uild secular-trend

models +Greiner and Gordon 66


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ithin the army, despite an o#ert shift in recruiting goals in 66 to targethigh school graduates +*unter and 0elson 67/8 Soldier Support Center 67/8 Dhite and *ose& 67/. Thus, shift in educational le#el ould not

seem to "e an important influence in the secular trends of army males.More specific cultural influences may "e acting in the case of Asian51acific Islander males. rom 6>> to 677 there as a significant in-crease in the num"er of foreign-"orn mem"ers of this group, causing a shiftfrom predominately American-"orn soldiers to predominantly foreign-"ornsolders, most of hom carne from the 1hilippines +Greiner and Gordon66/. The impact of this shift on stature trends in the %.S. Army Asian51a-cific su"group is readily seen in igure 4 and illustrates a classic case inhich the a#aila"le racial5ethnic classification is at too "road a le#el to pro-#ide sta"le estimates of future stature trends in this su"group. To impro#ethese estimates, population-specific data and models may "e re(uired for such heterogenous groups as Asian51acific Islanders, *ispanics, and 0ati#e

Americans. As indicated "elo, application of such models re(uires specificestimates of future minority group fre(uencies, and as :o"ert Dal&er haspointed out, their contri"ution to the army population is so small that theymay ha#e little impact on armyide parameter estimates regardless of theaccuracy of their indi#idual secular-trend models.

Model Applications

Models resulting from cultural filter research and su"group identifica-tions operate "y separately predicting #alues "y "irth-year cohort for eachdemographic su"group. These models assume "iocultural continuity ithineach of the demographic su"groups. 3stimates for future target populationsare "uilt "y com"ining indi#idual estimates for each su"group, eighted "y

appropriate demographic proportions. In this ay, population predictionschange according to their demographic ma&eup. An e)ample of this can "eseen "y predicting the mean #alues for stature of army males in the year /


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4< :AC3, 3T*0ICIT@, A0 *%MA0 30GI033:I0G

Table *Secular Trends in U.S. Army Male Stature

Trend

:acial53thnic Group +mm5cohortDhites 4.Blac&s .;>*ispanics =.4; Asian 1acific islanders -=.>;

@ear 1opulationa

Mean

Stature

677 Current 1opulation => mm

/


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Table )Accommodation :ro>ections for an Army 4elmeta

0o emographic Change More @ounger Cohorts

Si!e 677 /.

Dith no demographic change, e ould e)pect to see the mean #alue of

head "readth to decrease "y .> mm, head length to increase "y 4 mm and

head circumference "y ; mm. To of these changes are still "elo the

alloa"le o"ser#er error. @et, these small changes are so influential that the

current design could concei#a"ly fail to accommodate 4/ percent of the

target population. Thus, e#en unspectacular rates of change can interact

ith close-fitting designs and greatly influence the accommodation of future

target populations.

Conclusions

Applied secular-trend models are rarely "uilt from data gathered ith

the aim of model construction. *oe#er, the application of secular-trendmodels does not re(uire that all sources of change "e identified and under-

0A1A B%223TI0 4 4


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4/ :AC3, 3T*0ICIT@, A0 *%MA0 30GI033:I0G

stood. Instead, their application relies upon the assumption that past trends

ill continue finto the future. Because this assumption ill e#entually pro#e

false for any population, it is important to understand a model?s limitations

"efore it is applied. An understanding of the mechanisms that con-tri"ute tosecular trends merely pro#ides some a"ility to anticipate the sources of

insta"ility in the model. 'nce secular trends are modeled, hoe#er, their

rele#ance to design can only "e determined "y the sensiti#ity of the design

criteria.

:eferences Cited

Boc&, :. ., and :. C. Sy&es

676 3#idence for Continuing Secular Increase in *eight Dithin amilies in the %nitedStates. American ournal of *uman Biology E;4-;7.legal, J. M., D. :. *arlan, and . :. 2andis

677a Secular Trends in Body Mass Inde) and S&infold Thic&ness ith Socioeconomicactors in @oung Adult Men. American ournal of Clinical 0utrition ;7E=;;-==.

677" Secular Trends in Body Mass Inde) and S&infold Thic&ness ith Socioeconomicactors in @oung Adult Domen. American ournal of Clinical 0utrition ;7E=4=-=;4.

Garn, S. M., S. M. Bailey, 1. 3. Cole, and I. T. T. *iggins6 2e#el of 3ducation, 2e#el of Income, and 2e#el of atness in Adults. American ournal

of Clinical 0utrition 4


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Dhite, . 1., and . :. *ose&67/ The Analysis of Military Manpoer Issues. In Military Ser#ice in the %nited States.

3. Scocroft, ed. 1p. ;>. Technical :eport /-=-C3. 0atic&, MAE %.S. Army Huartermaster :esearch and 3ngineering Center.

0A1A B%223TI0 4 44

Documents

NAPA Bulletin 13 Gordon, Claire C. & Thomas M, Greiner – Biocultural Influences in the Analysis of Secular Trends. (Race, Ethnicity, And Human Engineering)