MILITARY MEDICINE, 169, 8:604, 2004 Stffing Model for Dentl Wellness nd Rediness Gurntor: LTC Jeffrey Chffin, DC USA Contributors: COL Lrry G. Rothfuss, DC USA* ; LCDR Scott A. Johnson, NC USN* ; MAJ Stephen D. Lrsen, MSC USAF* ; LTC Jeffrey Chffin, DC USA ; Kenn Finstuen, MSc Med PhD Orl helth is n integrl prt of generl helth. Previous reserch hs shown tht untreted orl conditions cn result in incresed rtes of disese nd nonbttle injury for deployed soldiers. The purpose of this study ws to develop models for U.S. Army dentl wellness nd rediness using multivrite regression nlysis pproch. Stffing levels nd dentl wellness nd rediness rtes were exmined for the first three qurters of fiscl yer 2002 t 40 Army instlltions. Full regression model equtions were developed for percent dentl wellness nd rediness using loction, time, dentl provider types, nd bsic trining instlltion s predictor vribles. Both models were shown to be sttisticlly significnt, with wellness R 2 0.37, F 12,107 5.18, p 0.001 nd rediness R 2 0.23, F 12,107 2.65, p 0.01. Further tests of specific predictor effects reveled tht wellness ws significntly ssocited with the specilties of generl dentistry, hygienists, nd orl surgery, nd tht rediness ws significntly ssocited with region nd the orl surgery specilty. Results my be useful for the U.S. Army to identify the best prctices in n effort to optimize dentl wellness nd rediness. Introduction rl helth is n importnt component of generl helth. The O U.S. Public Helth system hs worked diligently to identify trends in orl disese nd to work towrd mximizing ccess to orl helth cre in the United Sttes. Orl helth is lso n importnt component to overll militry rediness. Teweles nd King 1 studied the effects of poor dentl helth on the combt rediness of Army soldiers. They reported tht potentil dentl emergency conditions cn be ccurtely identified during routine dentl exmintions nd tht potentil emergency conditions result in significnt percentge of preventble dentl emergencies. An erlier study by Pyne nd Posey 2 reported tht in prolonged field trining exercise, dentl emergencies re responsible for considerble loss of duty time, with 74% of these emergencies viewed s preventble. More recently, Chffin et l. 3 reported tht dentl emergencies continue to threten the rediness of troops in deployed environments. Orl helth nd its reltionship to one s generl helth nd well-being hs gined incresed ttention in recent yers. The U.S. Surgeon Generl commissioned n evidence-bsed review *Administrtion, U.S. Army Medicl Deprtment Center nd School, 3151 Scott Rod, Fort Sm Houston, TX 78234. U.S. Army Dentl Commnd, 2050 Worth Rod, Suite 4, Fort Sm Houston, Sn Antonio, TX 78234. Professor of Helth Cre Administrtion, U.S. Army-Bylor Helthcre Administrtion Progrm, Fort Sm Houston, TX 78234. Msters degree students in the U.S. Army-Bylor University Grdute Progrm in Helth Cre. The views expressed in this rticle re those of the uthors nd do not reflect the officil policies of the Deprtment of the Army, the Deprtment of the Nvy, the Deprtment of the Air Force, the Deprtment of Defense, or the U.S. government. This mnuscript ws received for review in June 2003. The revised mnuscript ws ccepted for publiction in September 2003. of the orl helth of the Americn popultion nd in 2000 relesed the results in report entitled Orl Helth in Americ: A Report of the Surgeon Generl. 4 The report confirmed tht n individul s orl helth ws reflection of their generl helth nd qulity of life nd tht U.S. citizens could not be considered helthy without orl helth. The report identified further negtive effects on one s self-esteem, socil reltions, eduction, creer chievement, nd emotionl stte when orl helth is lcking. The report lso confirmed erlier findings tht, in generl, the orl helth of U.S. citizens hs improved, but there re significnt disprities in orl helth bsed on rce, income, geogrphy, nd socioeconomic levels. U.S. ntionl helth gols re trnslted to the populce vi Helthy People gols. The overrching gol of Helthy People 2010 is to reduce helth disprities 5 nd the report documented orl helth s focus re. The importnce of the Helthy People 2010 gend is tht it identifies the most significnt nd preventble threts to helth nd it focuses the public nd privte sectors efforts in ddressing helth disprities. The Orl Helth in Americ nd Helthy People 2010 reports confirmed the findings of numerous studies tht disproportionte number of U.S. citizens re plgued by orl nd dentl diseses nd re unble to rech even mrginl levels of orl helth. Access to preventive nd routine dentl cre plys vitl role in chieving orl helth. Mertz nd O Neil 6 provided evidence of the growing concern of unmet dentl helth needs mong U.S. citizens. The uthors found bundnt evidence tht sizble segment of the popultion does not hve ccess to privte cre, while the dentl sfety net is poorly defined nd underdeveloped. Reports on rmed forces dentl helth concerns re not restricted to the United Sttes or to Army personnel. Poor orl helth is concern for foreign rmed forces nd brnches of militry service other thn the Army. Deutsch nd Simecek 7 studied deployed U.S. Mrines during Opertions Desert Shield/Storm, nd Mhoney nd Coombs 8 provided literture review of dentl csulty rtes of U.S. nd foreign militry personnel in recent wrs, conflicts, nd deployments. The slient point found in both rticles is tht dentl emergencies during deployment occur more frequently when service members hve poor orl helth before deployment. Ensuring tht dentl conditions re corrected during the predeployment phse nd emphsizing the importnce of orl helth mintennce should reduce the incidence nd frequency of dentl emergencies in the re of opertions. The U.S. Army s Orl Helth Mintennce Progrm ws implemented in 1987. This progrm evolved from the reliztion tht proctive efforts to monitor nd tret soldiers could minimize disese nd nonbttle injuries during contingency opertions. To be proctive, soldiers need their dentl conditions screened routinely so tht dentl problems cn be identified nd 604
Stffing Model for Dentl Wellness nd Rediness corrected. Helth Affirs Policy 98-021 requires tht ctive duty nd selected reserve service members hve n nnul dentl exmintion. 9 Bsed upon the findings of this exmintion, service members re clssified into one of four fitness ctegories. The dentl fitness clssifictions hve been stndrdized for ll militry services in Helth Affirs Policy 02-011. 10 The respective ctegories re clss 4, nondeployble with no exmintion documented within the pst 12 months; clss 3, nondeployble without tretment for urgent conditions tht likely will cuse dentl emergency within 6 months; clss 2, worldwide deployble with need for nonurgent routine tretment; nd clss 1, worldwide deployble with no further tretment required. Deployble refers to service member being sttioned in n overses loction or in combt sitution. Helth Affirs Policy 96-024 requires tht ech instlltion mintin t lest 95% of its ssigned soldiers in dentl fitness clss 1 or 2. 11 The Tri-Service Dentl Chiefs hve lso set 60% gol for ssigned service members to be in dentl fitness clss 1. Within the Army, chieving the level of dentl fitness ctegory 2 is known s dentl rediness, s in redy for deployment. The Army refers to dentl fitness clss 1 s dentl wellness, nd the Nvy nd Air Force refer to clss 1 s orl helth. It is constnt chllenge for dentl providers nd militry units to chieve the desired stte of 95% dentl rediness nd, prticulrly, 60% wellness. In civilin smple, Woolfolk et l. 12 found correltions between dentl checkup behviors nd specific vribles. Gender, income, n ssocition with usul loction for dentl cre, nd the level of dentl nxiety were ll sttisticlly significnt vribles in determining ptient s desire to obtin dentl exmintion. Mnski nd Moeller 13 nlyzed the use of dentl services by providers, procedures, nd visits. The impliction of this study ws tht by developing better understnding of utiliztion, the dentl cre system could better provide for the demnds of the Americn dentl ptient. The uthors stted tht preventive services comprised the vst mjority of demnded dentl services such s exmintions nd clenings. Among specilty provider types, orl surgeon use ws higher in comprison to severl other dentl specilists nd suggested reltively high demnd for orl nd mxillofcil surgicl services. The purpose of this study ws to identify whether reltionship exists between stffing levels of dentl providers in Army dentl clinics to the dentl rediness nd wellness of Army soldiers. Mterils nd Methods Smple nd Dt Stffing levels nd dentl rediness nd wellness dt were collected from 40 U.S. Army instlltions with dentl tretment fcilities for the first three qurters of fiscl yer 2002. The U.S. Army Dentl Commnd, Fort Sm Houston, Sn Antonio, Texs, provided the dt. Dentl rediness nd wellness dt were extrcted from the Corporte Dentl Appliction, World Wide Web-bsed system tht trcks rediness nd worklod for Army dentl clinics. The Dentl Commnd Assistnt Chief of Stff for Clinicl Services provided stffing dt. Fcilities rnged in size from 2 to 114 dentl providers. Ech fcility ws ctegorized into one of six regions tht correspond to the six Army Regionl Dentl Commnds (RDCs). In this report, the RDCs will be referred to s RDC 1, RDC 2, etc. Some smller fcilities dt were ggregted to lrger fcilities to id dt nlysis; this occurred minly for posts in Europe. At the time of this study, fourth qurter dt were not yet vilble. To control for time-relted differences in the dt, three dummy vribles were creted to specify the qurter in which the dt were collected. With no missing dt, the smple size ws 120 events (n 120). Dt were not specific to the individul soldier level, nd ll ethicl considertions were followed. No dt were used tht could provide personl identifiction. Opertionl Definitions of Vribles Multivrite models were produced to estimte dentl wellness nd rediness, s well s to mesure the unique effects of ech predictor on the orl helth models. Two generl liner regression model equtions were creted: one for dentl wellness nd one for dentl rediness. Wellness, the desired dentl clss, ws opertionlly defined by the totl number of soldiers in dentl clss 1 divided by the totl number of soldiers t the Army instlltion. Dentl rediness includes soldiers in clss 1 nd clss 2 divided by the totl number of soldiers t the instlltion. Independent vribles were the sme for ech model nd reflected dentl provider types, bsic trining instlltions, time frmes, nd geogrphic regions. Types of providers included generl dentists, hygienists, orl surgeons, nd endodontists. A bsic trining dummy vrible ws creted to control for the worklod of new recruits nd their potentil incresed orl nd dentl needs required to bring the soldiers up to Army stndrds. Time frmes were defined s qurters nd indicted 3-month period in fiscl yer 2002. Geogrphic regions were consistent with the terminology used nd defined by the U.S. Army Medicl nd Dentl Commnds. Throughout this rticle, we refer to ech commnd s RDC nd specify ech s 1 through 6. This designtion protects the nonymity of specific region. The RDCs re geogrphiclly distinct nd the uthors know their identities. Investigtive Method For ech of the two models, multiple regressions were clculted using SPSS for Windows, Relese 11.0.1 (Chicgo, IL) 14 to determine the unique effects of ech independent vrible on the overll mount of shred vrince inherent in the generl model. The R 2 from ech full regression model served s bseline. Subsequent regressions were ccomplished, ech removing one independent vrible to determine the reduced R 2.On ech subsequent regression, the previously removed vribles were returned to the eqution to isolte the uniquely ttributble difference of ech vrible, ceteris pribus. F rtio tests were computed for ech effect to determine levels of sttisticl significnce. Results 605 The nlyses demonstrted tht there were differences in dentl rediness nd wellness rtes mong the RDCs. Dentl wellness rnged from 20.76% for RDC 1 to 28.22% for RDC 2,
606 Stffing Model for Dentl Wellness nd Rediness nd dentl rediness rnged from 91.05% for RDC 3 to 96.77% for RDC 4. The descriptive sttistics tht summrize the dentl wellness nd rediness t ech of the six U.S. Army Regionl Dentl Commnds re reported in Tble I. The number of soldiers nd their dentl clssifiction ctegory were verged by qurter. The percentge of well nd percentge of redy were clculted by dividing the verge number in ech respective dentl clss by the verge number of soldiers. For comprison purposes, the verge dentl rediness nd wellness figures were 93.01 nd 29.95%, respectively. Hving the pproprite number of dentl providers is n importnt prt of soldiers being ble to ccess the dentl cre system. Tble II displys the men number of providers per RDC strtified by dentl specilty. It lso compres the dentl stffing of bsic trining sites to nonbsic trining sites. Sttisticl nlysis ws performed to see whether differences exist between provider stffing t bsic versus nonbsic trining sites, but the descriptive sttistics would suggest tht there is not positive reltionship. The following is the rnge of the men number of dentl providers for ech of the dentl specilties exmined in this study: generl dentists (8.60 51.33), hygienists (3.40 14.33), endodontists (0.40 2.00), nd orl surgeons (1.55 3.00). Model Anlysis Inferentil sttistics from the multiple regression nlysis for wellness nd rediness re rryed in Tble III. Wellness regressions, s might be expected, reveled tht the provider ctegories of generl dentist nd hygienist hd sttisticlly significnt effects on the shred vrince. The model lso showed tht the orl surgeon specilty ws significnt predictor for orl wellness. The foundtion of the orl surgery specilty is the prctice of removing wisdom teeth nd nonrestorble teeth, the correction of trumtic injuries nd fcil deformities, s well s rnge of other tretments. This could potentilly bring soldier from ny dentl ctegory ll the wy up to clss 1 depending on the dentl helth of the soldier. For rediness, the model found tht orl surgery is lso strong predictor. A surprising finding to the investigtors ws tht the RDC ws significnt predictor for rediness. This suggests tht the region where soldiers re ssigned directly influences their dentl clssifiction. Discussion This nlysis demonstrtes the unique effects tht the independent vribles hve on the vrince in the dentl wellness nd rediness models. It further delinetes the importnce of selected specilist stffing ptterns nd the impct tht they cn hve on soldiers nd their dentl clss. Regrding dentl rediness, the model indictes tht region nd orl surgeons re sttisticlly significnt fctors in obtining dentl fitness clss 2. This study revels tht four of six regions filed to chieve the Army s gol of 95% dentl rediness. Of the four regions filing to meet the stndrd, three provide dentl cre to fmily members of ctive duty service members. This my provide n opportunity for further study to determine the effects of fmily member cre. The inclusion of fmily members could potentilly decrese the dentl tretment providers cpcity to provide cre for ctive duty personnel. Another fctor tht is integrl to chieving dentl rediness is the vilbility of troops for their dentl ppointments. This issue involves opertionl tempo, or the time the service member is wy from grrison. RDCs with lrge numbers of combt or combt support soldiers my experience difficulty in providing cre to these individuls becuse of their unique missions. Confounding the sitution is the fct tht contingency opertions occur irregulrly nd cn be unpredictble becuse of world events. However, the dt controlled for three different qurters in one fiscl yer to ccount for sesonl vrince. Time periods were not found to be sttisticlly significnt. Regions filing to meet the rediness stndrd should exmine the fctors tht prevent their chievement. Among the fctors tht need to be ddressed on regionl bsis re ptient cse mix, demogrphics, productivity of individul providers, nd use of vilble ppointment time. Tht orl surgery tretment is sttisticlly significnt ppers to be n expected finding becuse of the need to remove nonre- TABLE I DESCRIPTIVE STATISTICS FOR PREDICTORS OF DENTAL WELLNESS AND READINESS GROUPED BY QUARTER, REGION, AND BASIC TRAINING Predictors Totl Soldiers Totl Well Percent Well Totl Redy Percent Redy Qurters Fiscl yer 2002 1 354,259 83,110 23.46 329,119 92.90 Fiscl yer 2002 2 362,982 84,652 23.32 335,549 92.44 Fiscl yer 2002 3 365,108 84,830 23.23 337,618 92.47 Regions RDC 1 307,578 63,845 20.76 281,618 91.56 RDC 2 166,027 46,848 28.22 153,599 92.51 RDC 3 254,372 62,173 24.44 231,608 91.05 RDC 4 46,604 12,020 25.79 45,100 96.77 RDC 5 215,135 48,445 22.52 203,458 94.57 RDC 6 92,633 19,261 20.79 86,903 93.81 Presence of bsic trining Bsic 101,874 27,602 27.09 94,323 92.59 No bsic 980,475 224,990 22.95 907,963 92.60 N 1,082,349.
Stffing Model for Dentl Wellness nd Rediness 607 TABLE II MEANS AND SDS FOR THE NUMBER OF DENTISTS ASSIGNED TO CLINICS BY SPECIALTY, REGION, AND PRESENCE OF BASIC TRAINING Dentl Specilties Generl Dentistry (n 629) Hygiene (n 244) Endodontics (n 48) Orl Surgery (n 87) Clinics Men SD Men SD Men SD Men SD Region RDC1 3 13.73 13.71 4.55 3.91 0.91 0.68 2.82 3.12 RDC2 3 51.33 8.76 14.33 2.78 2.00 0.00 2.33 0.50 RDC3 11 13.27 18.06 6.27 8.94 1.18 2.24 1.55 2.05 RDC4 2 16.00 9.86 6.00 5.48 1.00 1.10 3.00 3.23 RDC5 8 12.87 8.82 6.62 3.42 1.87 3.56 2.00 1.98 RDC6 5 8.60 8.70 3.40 2.13 0.40 0.83 2.00 3.14 Presence of bsic trining Bsic 5 14.10 5.98 5.60 3.74 1.00 0.00 2.00 0.65 No bsic 35 15.94 7.69 6.17 6.35 1.23 2.22 2.20 2.69 N 1,008 dentists. TABLE III INFERENTIAL STATISTICS FOR PREDICTORS OF DENTAL WELLNESS AND READINESS Wellness Effects Tested R 2 Full R 2 Reduced Difference df 1 df 2 F Full model 0.3675 0 0.3675 12 107 5.18 Qurter 0.3675 0.3674 0.0001 2 107 0.00 Region 0.3675 0.3065 0.0609 5 107 2.00 Bsic trining 0.3675 0.3647 0.0028 1 107 0.47 Specilty Generl dentistry 0.3675 0.2854 0.0820 1 107 13.88 Hygiene 0.3675 0.3307 0.0368 1 107 6.23 Endodontic 0.3675 0.3577 0.0098 1 107 1.66 Orl surgery 0.3675 0.2924 0.0751 1 107 12.70 Rediness Effects Tested R 2 Full R 2 Reduced Difference df 1 df 2 F Full model 0.2288 0 0.2288 12 107 2.65 b Qurter 0.2288 0.2254 0.0035 2 107 0.24 Region 0.2288 0.0688 0.1601 5 107 4.44 b Bsic 0.2288 0.2285 0.0003 1 107 0.05 Specilty Generl dentistry 0.2288 0.2220 0.0068 1 107 0.95 Hygiene 0.2288 0.2242 0.0046 1 107 0.64 Endodontics 0.2288 0.2276 0.0013 1 107 0.17 Orl surgery 0.2288 0.1721 0.0557 1 107 7.87 Sttisticl significnce of F rtio, p 0.001; b p 0.01. storble, mlpositioned, or impcted teeth. One of the most used dentl specilties in the civilin sector is orl surgery. 12 A service member s ge highly correltes with the eruption sequence of third molrs (wisdom teeth). This cretes need for orl surgicl intervention mong the pool of young dults ge 18 25 yers, which comprises lrge percentge of the ctive duty popultion. The use of generl dentists to provide orl surgicl tretment must not be overlooked. Generl dentists cn tret vrying levels of surgicl difficulty depending on their level of experience nd trining. The generl dentist is n djunct to the orl surgeons specilty services. However, in our study, generl dentists were not found to be sttisticlly significnt in the rediness model. This my present n opportunity for generl dentists to ugment orl surgeons to increse dentl rediness nd my wrrnt further study. Chnging the providers prctice my dversely ffect dentl wellness, but rediness is more importnt to the U.S. Army. Restortive dentistry is the gretest need to elevte soldier into the rediness dentl fitness ctegory, nd providing this cre is the primry responsibility of generl dentists. Wellness is chllenge for the U.S. Army Dentl Corps. No RDC chieved the 60% threshold for wellness. However, there were few instlltions tht exceeded 50% dentl wellness.
608 Stffing Model for Dentl Wellness nd Rediness These instlltions could serve s models for the Army Dentl Cre system to identify best prctices. However, we did find significnt correltions ssocited with the bility to crete dentl fitness clss 1. Three of the four types of providers were highly sttisticlly significnt in predicting the bility to obtin dentl wellness. If the U.S. Army is to increse rtes of dentl wellness, our study suggests tht better blnce must be struck between hygienists, generl dentists, nd orl surgeons, nd the service member s bility to receive cre from these providers. Other vribles did not ply role in predicting dentl fitness clss 1. The U.S. Army s focus should be to first meet the gol of 95% dentl rediness before ddressing widespred nd unmet levels of dentl wellness. Specultion on why soldiers do not convert from dentl clss 2 to clss 1 is uncler, but it my likely be becuse of high demnd for finite mount of cre or the inbility to receive dentl cre becuse of the opertionl tempo of service member s orgniztion. Restortive dentistry nd prophylxis re the most needed cre to convert soldiers from clss 2 to 1. Cution should be used in the interprettion of these results becuse of limittions of the study. Only 9 months of dt were nlyzed. In ech qurter, there ws the potentil for stffing fluctutions, which my hve skewed the dt. The full models shred vrince only ccounts for 37% nd 23% of the totl vrince, respectively. For this reson, other fctors such s stffing rtios, provider type mix, nd deployments my explin greter shred vrince nd should be considered in subsequent studies. Severl other fctors re worth considertion. Dentl residency progrms my influence results becuse of personnel stffing nd trining requirements for residents nd their mentors. All RDCs hve residency progrms nd the effect of different progrms is unknown. Also, the specilty of generl dentistry my be further delineted mong vrious levels of postgrdute trining. These levels rnge from no postgrdute trining to 2-yer postgrdute trining progrms. This suggests vribility in the knowledge nd bility mong the generl dentists. A generl dentist with 2-yer dvnced trining progrm, for exmple, my be ble to supplement other types of dentl specilists. Unfortuntely, these dt were not collected, but my provide the bsis for n dditionl study. The findings of this study should not infer the importnce of ny single vrible. Determining proper dentl stff models requires dditionl decision criteri. These results simply show tht by controlling for worklod, time frme, nd loction, the right combintion of dentl providers cn hve n impct on rediness nd wellness. Dentl rediness is vitl to the U.S. Army. With tody s world sitution, the possibility of rpid militry intervention is relity nd it behooves the Army nd its service members to be dentlly redy. These models provide predictors tht my ssist the U.S. Army in chieving soldier dentl rediness nd wellness. The scope of this study is to provide models for dentl rediness nd wellness. These models will prove successful if they ssist in providing bseline for the lloction nd proper rrying of dentl providers. With this study s findings, the U.S. Army my better lign its resources to optimlly meet the dentl needs of its service members. References 1. Teweles RB, King JE: Impct of troop dentl helth on combt rediness. Milit Med 1987; 152: 233 5. 2. Pyne TF, Posey WR: Anlysis of dentl csulties in prolonged field trining exercises. Milit Med 1981; 146: 265 71. 3. Chffin J, King JE, Fretwell LD: U.S. Army dentl emergency rtes in Bosni. Milit Med 2000; 166: 1074 8. 4. U.S. Deprtment of Helth nd Humn Services: Orl helth in Americ: report of the Surgeon Generl executive summry, 2000. Avilble t http://www. nidcr.nih.gov/sgr/execsumm.htm; ccessed December 6, 2002. 5. U.S. Deprtment of Helth nd Humn Services: Helthy People 2010 fct sheet, 2000. Avilble t http://odphp.osophs.dhhs.gov/pubs/hp2000/hp2kfct.htm; ccessed November 30, 2002. 6. Mertz E, O Neil E: The growing chllenge of providing orl helth cre services to ll Americns. Helth Affirs 2002; 21: 75 7. 7. Deutch WM, Simecek JW: Dentl emergencies mong mrines shore in Opertions Desert Shield/Storm. Milit Med 1996; 161: 620 3. 8. Mhoney GD, Coombs M: A literture review of dentl csulty rtes. Milit Med 2000; 165: 751 6. 9. Deprtment of Defense (Helth Affirs): Policy on uniformity of dentl clssifiction system, frequency of periodic dentl exmintions, ctive duty overses screening, nd dentl deployment stndrds. Helth Affirs policy letter 98-021, 1998. 10. Deprtment of Defense (Helth Affirs): Policy on stndrdiztion of orl helth nd rediness clssifictions. Helth Affirs policy letter 02-011, 2002. 11. Deprtment of Defense (Helth Affirs): Policy on inclusion of dentistry in TRICARE regions. Helth Affirs policy letter 96-024, 1996. 12. Woolfolk MW, Lng P, Borgnkke WS, Tylor GW, Ronis DL, Nyquist LV: Determining dentl checkup frequency. J Am Dent Assoc 1999; 130: 715 23. 13. Mnski RJ, Moeller JF: Use of dentl services: n nlysis of visits, procedures nd providers. J Am Dent Assoc 2002; 133: 167 75. 14. SPSS, Inc.: SPSS, Bse 11.0.1. Chicgo, IL, SPSS, Inc., 1999.