Methods for the Dartmouth Atlas of Health Care Report · The Dartmouth Atlas uses ZIP Codes as the fundamental geographic identifier of Medicare beneficiaries. We approximated AF4Q

Methods for the Dartmouth Atlas of Health Care Report:

Regional and Racial Variation in Health Care among Medicare Beneficiaries

prepared for

The Robert Wood Johnson Foundation Aligning Forces for Quality program

December 2008

Elliot Fisher, MD MPH

David Goodman, MD MS

Amitabh Chandra, PhD

Kristen Bronner, Editor

with the assistance of the Dartmouth Atlas of Health Care working group

For more information, visit http://www.dartmouthatlas.org/af4q.shtm

Document description: This technical document provides a description of the methods used for the Dartmouth Atlas Report, Regional and Racial Variation in Health Care among Medicare Beneficiaries and the accompanying measures. The document is divided into three sections. In the first section, descriptions of each measure are provided, including the numerators and denominators. The second section gives the ZIP codes defining the Aligning Forces for Quality (AF4Q) regions. The third section provides a formal description of the methods used to calculate confidence intervals. Other resources can be found at http://www.dartmouthatlas.org/af4q.shtm. These include Frequently Asked Questions and tables containing the five measures, with their corresponding confidence intervals. A word about the precision of Atlas measures: The Atlas team has taken care to prepare measures of reasonable precision and to provide the necessary supporting information that allows users to judge the likely importance of differences in rates and proportions. The denominators differ widely, depending on the measure and the region. For some measures (e.g. ambulatory care-sensitive condition discharges), the entire fee-for-service Medicare population is the denominator. For other indicators, such as those for diabetics, the denominators are obviously much smaller. Stratification by race leads to especially small denominators in some regions. To prevent misinterpretation of the significance of differences in rates and proportions, we have suppressed any measure with a denominator of less than 200. Even with this suppression, a rate that differs across regions or race cannot be assumed to be statistically significant or clinically important. Confidence intervals (95%) are provided at http://www.dartmouthatlas.org/af4q.shtm to guide users’ interpretation. Although these are not formal inferential tests, non-overlapping confidence intervals generally mean that it is unlikely that the differences occurred by chance. The reader must be cautious in making multiple comparisons where differences may be found even if occurring by chance. It is equally important to interpret the clinical or policy significance of differences. If an observed difference in rates is not important (particularly when including the range of the confidence intervals), then a statistical test of the difference is moot.

Section I. Definition of Measures

Measure: Leg amputationLast revised: 10/6/08Faculty: GoodmanStatistical analyst/programmer: Steph; Zhao

Description: Defined as average rate of leg amputations.

Time period: 2003-06, 2003-04, 2005-06

Population: Medicare, non-HMO, age 65 - 99 (mid-year), 100% sample; Part A eligibility

Event: ICD-9: procedures 84.15 to 84.17

Rates: Overall, blacks, and non-blacks

Adjustment: Age, sex, race indirect adjustment

Geographies: States, AF4Q regions, HRRs, HSAs

Measure: Ambulatory care-sensitive condition discharge rateLast revised: 10/6/08Faculty: GoodmanStatistical analyst/programmer: Steph; Zhao

Description:

Time period: 2003-06, 2003-04, 2005-06

Population: Medicare, non-HMO, age 65 - 99 (mid-year), 100% sample; Part A eligibility

Event:Any of the following Primary diagnosisA01 Convulsions 780.3xA02 COPD 491xx, 492xx, 494xx, 496xx, 466.0x

466.0x only w/secondary dx 491xx, 492xx, 494xx, 496xxA03 Pneumonia 481xx, 482.2x, 482.3x, 482.9x, 483xx, 485xx, 486xx

Excl. secondary dx 282.6xA04 Asthma 493xxA05 CHF 428xx, 402.01, 402.11, 402.91, 518.4x

Excl. sx 36.01, 36.02, 36.05, 36.1x,37.5x, or 37.7xA06 Hypertension 401.0x, 401.9x, 402.00, 402.10, 402.90

Excl. sx 36.01, 36.02, 36.05, 36.1x,37.5x, or 37.7xA07 Angina 411.1x, 411.8x, 413xx

Excl. sx 01-86.99A08 Cellulitis 681xx, 682xx, 683xx, 686xx

Excl. sx 01-86.99,except if 86.0x is the first and only sx codeA09 Diabetes 250.0x, 250.1x, 250.2x, 250.3x, 250.8x, 250.9xA10 Gastroent. 558.9xA11 Kidney/Urinary 590xx, 599.0x, 599.9xA12 Dehydration 276.5x


Adjustment: Age, sex, race indirect adjustment


Ambulatory care sensitive condition discharge rate. Note this uses the Dartmouth Atlas definition and may differ from other commonly used definitions.

Measure: Diabetic receiving HgbA1C testLast revised: 10/30/08Faculty: GoodmanStatistical analyst/programmer: Steph; Weiping

Description:

Time period: 2003-06, 2003-04, 2005-06

Population: Non-HMO Medicare, age 65 - 75 (December 31) with Parts A & B eligibility, 20% sample.Diabetes definition:ICD-9 codes: 250, 357.2, 362.0, 366.41, 648.0: DRGs 294, 295.Outpatient/nonacute inpatient CPT codes: 92002-92014, 99201-99205, 99211-99215, 99217-99220, 99241-99245, 99271-99275, 99301-99303, 99311-99313, 99321-99323, 99331-99333, 99341-99355, 99384-99387, 99394-99397, 99401-99404, 99411, 99412, 99420, 99429, 99499.Acute inpatient/emergency department CPT codes: 99221-99223, 99231-99233, 99238-99239, 99251-99255, 99261-99263, 99281-99285, 99291-99292, 99356-99357.

Event: CPT code: 83036


Adjustment: None


Defined as the occurrence of at least one HgbA1c event during the measurement year to a person with a diabetes diagnosis. Diabetes diagnosis: two face-to-face encounters with different dates of service in an ambulatory setting or nonacute inpatient setting or one face-to-face encounter in an acute inpatient or emergency room setting during measurement year or prior year.

Measure: Diabetic receiving blood lipids testLast revised: 10/30/08Faculty: GoodmanStatistical analyst/programmer: Steph; Weiping

Description:

Time period: 2003-06, 2003-04, 2005-06


Event: CPT codes: 80061, 83715, 83716, 83721


Adjustment: None


Defined as the occurrence of at least one blood lipids (LDL_C) test during the year to a person with a diabetes diagnosis. Diabetes diagnosis: two face-to-face encounters with different dates of service in an ambulatory setting or nonacute inpatient setting or one face-to-face encounter in an acute inpatient or emergency room setting during measurement year or prior year.

Measure: Diabetic receiving eye examinationLast revised: 10/30/08Faculty: GoodmanStatistical analyst/programmer: Steph; Weiping

Description:

Time period: 2003-06, 2003-04, 2005-06


Event: ICD-9 codes: 14.1-14.5, 14.9, 95.02-95.04, 95.11, 95.12, 95.16V code: V72.0CPT codes: 67101, 67105, 67107-67108, 67110, 67112, 67141, 67145, 67208, 67210, 67218, 67227, 67228, 92002, 92004, 92012, 92014, 92018, 92019, 92225, 92226, 92230, 92235, 92240, 92250, 92260, 92287, 99203- 99205, 99213-99215, 99242-99245


Adjustment: None


Defined as the occurrence of an eye exam during the measurement year. This includes diabetics who had one of the following:• a retinal or dilated eye exam by an eye care professional (optometrist or ophthalmologist) in the measurement year• a negative retinal exam (no evidence of retinopathy: ICD-9 codes 250.5, 362.01-362.07) by an eye care professional in the year prior to the measurement year. Diabetes diagnosis: two face-to-face encounters with different dates of service in an ambulatory setting or nonacute inpatient setting or one face-to-face encounter in an acute inpatient or emergency room setting during measurement year or prior year.

Section II. Dartmouth Atlas Definition of AF4Q Regions The Dartmouth Atlas uses ZIP Codes as the fundamental geographic identifier of Medicare beneficiaries. We approximated AF4Q county-based regions by linking to ZIP Codes. NOTE: three AF4Q regions represent entire states, so a ZIP code list is not given. These are Maine (518 ZIP codes), Minnesota (1,037 ZIP codes) and Wisconsin (905 ZIP codes).

AF4Q NameNumber ofZIP Codes ZIP Codes

A01 CINCINNATI, OH 229 41001 45032 45135 45221 4529841005 45033 45138 45222 4529941007 45034 45140 45223 4561641010 45036 45142 45224 4561841011 45039 45144 45225 4565041012 45040 45145 45226 4566041014 45041 45146 45227 4567941015 45042 45147 45228 4569341016 45043 45148 45229 4569741017 45044 45150 45230 4594441018 45050 45152 45231 4595041019 45051 45153 45232 4599941022 45052 45154 45233 4700141030 45053 45155 45234 4700641035 45054 45156 45235 4701741042 45055 45157 45236 4701841046 45056 45158 45237 4702141048 45061 45159 45238 4702241051 45062 45160 45239 4702341052 45063 45162 45240 4702541053 45065 45164 45241 4703141054 45066 45166 45242 4703241059 45067 45167 45243 4703341063 45068 45168 45244 4703441071 45069 45169 45245 4703741072 45071 45171 45246 4703941073 45073 45172 45247 4704141074 45099 45174 45248 4704241075 45101 45176 45249 4706041076 45102 45177 4525041080 45103 45201 4525141085 45105 45202 4525241091 45106 45203 4525341092 45107 45204 4525441094 45110 45205 4525541097 45111 45206 4525841099 45112 45207 4526245001 45113 45208 4526345002 45114 45209 4526445004 45115 45210 4526745005 45118 45211 4526845011 45119 45212 4526945012 45120 45213 4527045013 45121 45214 4527145014 45122 45215 4527345015 45123 45216 4527445018 45130 45217 4527545025 45131 45218 4527745026 45132 45219 4528045030 45133 45220 45296


A02 CLEVELAND, OH 65 44017 4414744022 4414944040 4417844070 4418144101 4418544102 4418844103 4418944104 4419044105 4419144106 4419244107 4419344108 4419444109 4419544110 4419844111 441994411244113441144411544116441174411844119441204412144122441234412444125441264412744128441294413044131441324413344134441354413644137441384413944140441414414244143441444414544146


A03 DETROIT, MI 297 48001 48069 48124 48186 48240 4833548002 48070 48125 48187 48242 4833648004 48071 48126 48188 48243 4834048005 48072 48127 48189 48244 4834148006 48073 48128 48190 48255 4834248007 48074 48130 48191 48260 4834348009 48075 48131 48192 48264 4834648012 48076 48133 48193 48265 4834748014 48079 48134 48195 48266 4834848015 48080 48135 48197 48267 4835048017 48081 48136 48198 48268 4835348021 48082 48137 48201 48269 4835648022 48083 48138 48202 48272 4835748023 48084 48139 48203 48275 4835948025 48085 48140 48204 48277 4836048026 48086 48141 48205 48278 4836148027 48088 48143 48206 48279 4836248028 48089 48144 48207 48288 4836348030 48090 48145 48208 48301 4836648032 48091 48146 48209 48302 4836748033 48092 48150 48210 48303 4837048034 48093 48151 48211 48304 4837148035 48094 48152 48212 48306 4837448036 48095 48153 48213 48307 4837548037 48096 48154 48214 48308 4837648038 48097 48157 48215 48309 4837748039 48098 48158 48216 48310 4838048040 48099 48159 48217 48311 4838148041 48101 48160 48218 48312 4838248042 48102 48161 48219 48313 4838348043 48103 48162 48220 48314 4838648044 48104 48164 48221 48315 4838748045 48105 48165 48222 48316 4839048046 48106 48166 48223 48317 4839148047 48107 48167 48224 48318 4839348048 48108 48168 48225 48320 4839748049 48109 48169 48226 48321 4839848050 48110 48170 48227 48322 4844248051 48111 48173 48228 48323 4846248054 48112 48174 48229 48324 4881648059 48113 48175 48230 48325 4883648060 48114 48176 48231 48326 4884348061 48115 48177 48232 48327 4884448062 48116 48178 48233 48328 4885548063 48117 48179 48234 48329 4886348064 48118 48180 48235 48330 4926748065 48120 48182 48236 48331 4927048066 48121 48183 48237 4833248067 48122 48184 48238 4833348068 48123 48185 48239 48334


A04HUMBOLDT COUNTY, CA 41 00050

00054955019550295503955119551495518955199552195524955259552695528955349553695537955409554295545955469554795549955509555195553955549555595556955589555995560955629556395564955659556995570955719557395589


A05 KANSAS CITY, MO 182 64013 64114 64179 6620364014 64116 64180 6620464015 64117 64183 6620564016 64118 64184 6620664018 64119 64185 6620764024 64120 64187 6620864028 64121 64188 6620964029 64123 64190 6621064030 64124 64191 6621164034 64125 64192 6621264048 64126 64193 6621364050 64127 64194 6621464051 64128 64195 6621564052 64129 64196 6621664053 64130 64197 6621764054 64131 64198 6621864055 64132 64199 6621964056 64133 64439 6622064057 64134 64444 6622164058 64136 64999 6622264060 64137 66012 6622364063 64138 66018 6622464064 64139 66019 6622564065 64141 66021 6622664066 64144 66030 6622764068 64145 66031 6625064069 64146 66051 6625164070 64147 66061 6627664072 64148 66062 6628264073 64149 66063 6628364075 64150 66083 6628564079 64151 66085 6628664081 64152 6610164082 64153 6610264086 64154 6610364087 64155 6610464088 64156 6610564089 64157 6610664092 64158 6610964098 64160 6611064101 64161 6611164102 64163 6611264105 64164 6611364106 64165 6611564108 64166 6611764109 64167 6611864110 64168 6611964111 64170 6616064112 64171 6620164113 64172 66202


A07 MEMPHIS, TN 83 37501 3814137544 3814238002 3814538014 3814638016 3814738017 3814838018 3815038027 3815138028 3815238029 3815738053 3815938054 3816138055 3816338083 3816538088 3816638101 3816738103 3816838104 3817338105 3817438106 3817538107 3817738108 3818138109 3818238111 3818338112 3818438113 3818638114 3818738115 3818838116 3819038117 3819338118 3819438119 3819538120 381973812238124381253812638127381283812938130381313813238133381343813538136381373813838139


A09 PUGET SOUND 293 98001 98057 98134 98259 98372 9844698002 98058 98136 98270 98373 9844798003 98059 98138 98271 98374 9844898004 98061 98139 98272 98375 9845098005 98062 98141 98275 98378 9845598006 98063 98144 98287 98380 9846098007 98064 98145 98288 98383 9846498008 98065 98146 98290 98384 9846598009 98070 98148 98291 98385 9846698010 98071 98151 98292 98386 9846798011 98072 98154 98293 98387 9847198012 98073 98155 98294 98388 9847798013 98074 98158 98296 98390 9848198014 98075 98160 98303 98391 9849098015 98077 98161 98304 98392 9849298019 98082 98164 98310 98393 9849398020 98083 98165 98311 98394 9849698021 98087 98166 98312 98395 9849798022 98089 98168 98314 98396 9849898023 98092 98170 98315 98397 9849998024 98093 98171 98321 98398 9850198025 98101 98174 98322 98401 9850298026 98102 98175 98323 98402 9850398027 98103 98177 98327 98403 9850498028 98104 98178 98328 98404 9850598029 98105 98181 98329 98405 9850698030 98106 98184 98330 98406 9850798031 98107 98185 98332 98407 9850898032 98108 98188 98333 98408 9850998033 98109 98190 98335 98409 9851198034 98110 98191 98337 98411 9851298035 98111 98194 98338 98412 9851398036 98112 98195 98340 98413 9851698037 98113 98198 98342 98415 9853098038 98114 98199 98344 98416 9854098039 98115 98201 98345 98417 9855698040 98116 98203 98346 98418 9855898041 98117 98204 98348 98419 9857698042 98118 98205 98349 98421 9857998043 98119 98206 98351 98422 9858098045 98121 98207 98352 98424 9858998046 98122 98208 98353 98430 9859798047 98124 98213 98354 98431 9859998050 98125 98223 98359 9843398051 98126 98224 98360 9843898052 98127 98241 98364 9843998053 98129 98251 98366 9844298054 98131 98252 98367 9844398055 98132 98256 98370 9844498056 98133 98258 98371 98445


A10WILLAMETTE VALLEY, OR 229 00068 97109 97232 97329 97427

00069 97111 97233 97330 9743000070 97113 97236 97331 9743100077 97114 97238 97333 9743497002 97115 97239 97335 9743797004 97116 97240 97336 9743897005 97117 97242 97338 9743997006 97119 97251 97339 9744097007 97123 97253 97342 9744697008 97124 97254 97344 9744897009 97125 97255 97345 9745197010 97127 97258 97346 9745297011 97128 97266 97347 9745397013 97132 97267 97348 9745497014 97133 97268 97350 9745597015 97137 97269 97351 9745697017 97140 97271 97352 9746197019 97144 97280 97355 9746397020 97148 97281 97358 9747297022 97200 97282 97359 9747797023 97201 97283 97360 9747897024 97202 97286 97361 9748097026 97203 97290 97362 9748297027 97204 97291 97370 9748797028 97205 97292 97371 9748897030 97206 97293 97373 9748997032 97207 97294 97374 9749097034 97208 97296 97375 9749297035 97209 97298 97377 9749397036 97210 97299 9737897038 97211 97301 9738197042 97212 97302 9738397045 97213 97303 9738497049 97214 97304 9738597055 97215 97305 9738697060 97216 97306 9738997062 97217 97307 9739297067 97218 97308 9739697068 97219 97309 9740197070 97220 97310 9740297071 97221 97311 9740397075 97222 97312 9740497076 97223 97313 9740597077 97224 97314 9740897078 97225 97317 9740997080 97227 97321 9741297086 97228 97322 9741397089 97229 97324 9741997101 97230 97325 9742497106 97231 97327 97426


A11 WESTERN MICHIGAN 183 48809 49316 49417 4950848811 49317 49418 4950948812 49318 49419 4951048815 49319 49420 4951248818 49320 49421 4951448829 49321 49422 4951548834 49322 49423 4951648838 49323 49424 4951848845 49325 49425 4951948846 49326 49426 4952348849 49327 49427 4952548850 49328 49428 4952848851 49329 49429 4953048852 49330 49430 4953448860 49331 49431 4954448865 49332 49434 4954648870 49333 49435 4954848875 49335 49436 4955048881 49336 49437 4955548884 49337 49440 4956048885 49338 49441 4958848886 49339 49442 4959948887 49340 49443 4962348888 49341 49444 4963148891 49342 49445 4963948897 49343 49446 4964249010 49344 49448 4964449021 49345 49449 4965549035 49346 49450 4965649046 49347 49451 4966549050 49348 49452 4967749058 49349 49453 4967949060 49351 49454 4968849070 49355 4945549073 49356 4945649078 49357 4945749080 49401 4945849301 49402 4945949302 49403 4946049303 49404 4946149304 49405 4946349305 49406 4946449306 49408 4946849307 49409 4950149309 49410 4950249310 49411 4950349311 49412 4950449312 49413 4950549314 49415 4950649315 49416 49507


A12 WESTERN NEW YORK 257 14001 14069 14169 14301 14729 1481314004 14070 14170 14302 14730 1482214005 14072 14171 14303 14731 1483614006 14075 14172 14304 14732 1488014008 14080 14173 14305 14733 1488414009 14081 14174 14411 14735 1489514010 14082 14201 14416 14736 1489714011 14083 14202 14422 1473714012 14085 14203 14427 1473814013 14086 14204 14429 1473914020 14091 14205 14452 1474014021 14092 14206 14470 1474114024 14094 14207 14476 1474214025 14095 14208 14477 1474314026 14098 14209 14479 1474414027 14101 14210 14482 1474514028 14102 14211 14525 1474714029 14103 14212 14530 1474814030 14105 14213 14536 1475014031 14107 14214 14549 1475114032 14108 14215 14550 1475214033 14109 14216 14557 1475314034 14110 14217 14569 1475414035 14111 14218 14571 1475514036 14112 14219 14591 1475614037 14113 14220 14701 1475714038 14120 14221 14702 1475814039 14125 14222 14703 1476014040 14126 14223 14704 1476614041 14127 14224 14706 1476714042 14129 14225 14707 1476914043 14130 14226 14708 1477014047 14131 14227 14709 1477214048 14132 14228 14710 1477414051 14133 14231 14711 1477514052 14134 14233 14712 1477714054 14135 14240 14714 1477814055 14136 14241 14715 1477914056 14138 14260 14716 1478114057 14139 14261 14717 1478214058 14140 14263 14718 1478314059 14141 14264 14719 1478414060 14143 14265 14720 1478514061 14144 14267 14721 1478614062 14145 14269 14722 1478714063 14150 14270 14723 1478814065 14151 14272 14724 1480214066 14166 14273 14726 1480314067 14167 14276 14727 1480414068 14168 14280 14728 14806


A14SOUTH CENTRAL PENNSYLVANIA 68 17019 17363

17301 1736417302 1736517303 1736617304 1736817306 1737017307 1737117309 1737217310 1737517311 1740117312 1740217313 1740317314 1740417315 1740517316 1740617317 1740717318 1740817319 174151732017321173221732317324173251732617327173291733117332173331733417337173391734017342173431734417345173471734917350173521735317354173551735617358173601736117362

28 REGionAl AnD RACiAl VARiAtion in HEAltH CARE AmonG mEDiCARE BEnEFiCiARiES

Community Counties

Cincinnati, OH In Ohio

Hamilton County

Clermont County

Warren County

Butler County

Brown County

Adams County

Clinton County

Highland County

In Kentucky

Boone County

Kenton County

Campbell County

Grant County

In Indiana

Dearborn County

Ripley County

Cleveland, OH Cuyahoga County

Detroit, MI Wayne County

oakland County

macomb County

St. Clair County

livingston County

Washtenaw County

monroe County

Humboldt County, CA Humboldt County

Kansas City, MO In Kansas

Johnson County

Wyandotte County

In Missouri

Jackson County

Platte County

Clay County

Maine Statewide (all counties in the state)

Memphis, TN Shelby County

Minnesota Statewide (all counties in the state)

Aligning Forces for Quality Communities

Community Counties

Puget Sound King County

Kitsap County

Pierce County

Snohomish County

thurston County

Willamette Valley, OR multnomah County

Washington County

marion County

Polk County

Yamhill County

Clackamas County

linn County

Benton County

lane County

Western Michigan mason County

lake County

osceola County

oceana County

newaygo County

mecosta County

montcalm County

muskegon County

ottawa County

Kent County

ionia County

Allegan County

Barry County

Western New York Cattaraugus County

Alleghany County

Erie County

Genesee County

niagara County

orleans County

Wyoming County

Chautauqua County

Wisconsin Statewide (all counties in the state)

South Central Pennsylvania Adams County

York County

A DARtmoutH AtlAS PRoJECt REPoRt CommiSSionED FoR tHE AliGninG FoRCES FoR QuAlitY PRoGRAm 29

Cincinnati

Hospital Service Areas in the Cincinnati, Ohio AF4Q Region

AF4Q counties

Hospital service areas

Principal cities


Cleveland

Hospital Service Areas in the Cleveland, Ohio AF4Q Region

AF4Q counties


Principal cities


Detroit

Toledo

Hospital Service Areas in the Detroit, Michigan AF4Q Region

AF4Q counties


Principal cities


Eureka

Hospital Service Areas in the Humboldt County, California AF4Q Region

AF4Q counties


Principal cities


Kansas City, MO

Kansas City, KS

Hospital Service Areas in the Kansas City, Missouri AF4Q Region

AF4Q counties


Principal cities


Portland

Augusta

Hospital Service Areas in the Maine AF4Q Region


Principal cities


Memphis

Hospital Service Areas in the Memphis, Tennessee AF4Q Region

AF4Q counties


Principal cities


St.St.St.St.St.St.St.St.St.PaulPaulPaulPaulPaulPaulPaulPaulPaul

Minnea-Minnea-Minnea-Minnea-Minnea-Minnea-Minnea-Minnea-Minnea-polispolispolispolispolispolispolispolispolis

Hospital Service Areas in the Minnesota AF4Q Region


Principal cities


Olympia

Tacoma

Seattle

Hospital Service Areas in the Puget Sound, Washington AF4Q Region

AF4Q counties


Principal cities


Salem

Portland

Hospital Service Areas in the Willamette Valley, Oregon AF4Q Region

AF4Q counties


Principal cities


Lansing

GrandRapids

Hospital Service Areas in the Western Michigan AF4Q Region

AF4Q counties


Principal cities


Buffalo

Rochester

Hospital Service Areas in the Western New York AF4Q Region

AF4Q counties


Principal cities


Madison

Milwaukee

Hospital Service Areas in the Wisconsin AF4Q Region


Principal cities


York

Hospital Service Areas in the South Central Pennsylvania AF4Q Region

AF4Q counties


Principal cities

Section III. Calculation of Confidence Intervals

Calculating Confidence Intervals for Atlas Measures

Center for Health Policy Research, The Dartmouth Institute for Health Policy and

Clinical Practice, Dartmouth College, Hanover, NH, USA

May 6, 2008

Summary. This document provides a review of the methods used to calculate variances

(and standard errors) of indirectly standardized rates for count variables and continuous

variables. The methods may not be suitable for all situations for which confidence inter-

vals are sought, for example, proportions. However, counts and continuous variables are

the most common variables currently included in the Dartmouth Atlas for Health Care.

Calculating Confidence Intervals for Count Variables

The indirect standardized rate (ISR) for region i is calculated as:

ISRi = mOi

Ei

,

where m is the crude national rate (total number of events divided by the total popula-

tion), Oi is the observed count in region i and Ei is the expected count in region i. The

expected count in region i is calculated as

Ei =∑

j

nij × crude ratej,

where j is the stratum (say, age, sex or race).

The variance of the ISRi is then written

var(ISRi) =m2

E2i

var(Oi).

1

Table 1Example of 3 Region, 2 Age group indirect standardization; included are the population

counts (n), observed events (O) and expected events (E).

Region Age Population Observed Expected Sumi j nij Events Oij Events Eij Events Ei

1 1 100 5 10 32.52 200 15 22.5

2 1 100 10 10 32.52 200 30 22.5

3 1 200 25 20 652 400 45 45

In this calculation, we assume that var(Oi) = Oi (Poisson assumption) and Ei is constant.

The standard error is then

se(ISRi) =m

Ei

√Oi

The normal distribution-based 95% confidence interval is then

(ISRi − 1.96m

√Oi

Ei

, ISRi +1.96m

√Oi

Ei

).

Example

An example with 3 regions (i = 1, 2, 3) and 2 age groups (j = 1, 2) is used to illustrate

the principle. The counts are shown in Table 1. The population crude rate is m =5+15+10+30+25+45

100+200+100+200+200+400= 130

1200= 0.1083. The crude rate for crude ratej=1 = 5+10+25

100+100+200=

40400

= 0.1 and the crude rate for crude ratej=2 = 15+30+45200+200+400

= 90800

= 0.1125.

Using these calculations as a basis, ISRi=1 = 0.1083 2032.5

= 0.067, ISRi=2 = 0.1083 4032.5

=

0.133 and ISRi=3 = 0.10837065

= 0.117.

The standard errors are then se(ISR1) = 0.1083√

2032.5

= 0.015, se(ISR2) = 0.1083√

4032.5

=

0.021 and se(ISR3) = 0.1083√

7065

= 0.014. The 95% confidence intervals are then calcu-

lated as the ISRi plus and minus 1.96 times the standard error.

2

Calculating Confidence Intervals for Continuous Variables

Continuous variables include Atlas variables such as patient days or expenditures. Using

the same notation as above, the variance for continuous variables is written

var(ISRi) =m2

E2i

var(Oi).

However, we write the pooled variance (across all regions) var(Oi) as

var(Oi) = ni

regions∑i

(ni − 1)s2i∑

i(ni − 1)

= ni

((n1 − 1)s2

1∑i(ni − 1)

+(n2 − 1)s2

2∑i(ni − 1)

+(n2 − 1)s2

3∑i(ni − 1)

+ . . .

)

= nis2P

where ni is the number of people in the region i, s2i is the within region variance and

where the second term is often written as s2P , simplifying the the representation of the

pooled (weighted average) variance across regions.

Then, the standard error is written

se(ISRi) =msP

Ei

√ni,

and the normal distribution-based 95% confidence interval is then(ISRi −

1.96msP√

ni

Ei

, ISRi +1.96msP

√ni

Ei

).

Example

Expenditures for Region 1 have variance 6,000 and sample size 1,000. Meanwhile,

expenditures for Region 2 have variance 3,000 and sample size 2,000. The pooled estimate

of the variance is then written s2P = 1,000×6,000

3,000+ 2,000×3,000

3,000= 4, 000.

Now, if we assume the population crude mean expenditures (m) are 10,000, while

the observed expenditures in Region 1 (O1) are 8,000 and the expected expenditures

for Region 1 (E1) are 10,000, the adjusted expenditures for Region 1 are 10,000×8,00010,000

=

8, 000. The variance of expenditures for Region 1 is then calculated as 4,000m2√

1,000E2 =

126, 491. Alternatively, the standard error is 356 and the 95% confidence interval is then

(7302, 8698).

3

Documents

Methods for the Dartmouth Atlas of Health Care Report · The Dartmouth Atlas uses ZIP Codes as the fundamental geographic identifier of Medicare beneficiaries. We approximated AF4Q