Table 3.

Summary of multimorbidity instruments and their associations with outcomes measured from all the included studies

Multimorbidity measures	Association between outcomes and multimorbidity
	Evidence of an association	No evidence of an association
A=Count of individual conditions
DC (many different groupings ranging from 764 76 113 to 14766 conditions and some are further categorised21)	ADL limitations,43 activity limitations,52 affective well-being,126 cognitive function,82 continuity of care (3 years),105 deficits of perceived general health,104 depression,92 depressive symptoms,67 104 disability,17 65 84 85 emergency hospital admission (2 years),120 fall-related injuries,71 fall risk,76 frequency of contacts with physicians (1 year),116 functional capacity,93 functional decline (2 years),120 functional Impairment,111 functional limitations,74 future physical functioning,28 general health,52 healthcare costs,23 91 health-related quality of life,68 75 81 90 115 hospitalisation (3 years),18 hospital admissions (1 year),95 96 99 hospital outpatient visits (1 year),114 hospitalisation/emergency department visits,114 life satisfaction,22 mental distress,52 mortality (1 year),99 (3 years),18 48 (5 years),110 (10 years),28 number of contacts with general practice (1 year),117 number of medications prescribed (1 year),117 number of mentally unhealthy days,43 44 number of physically unhealthy days,43 44 number of different ambulatory physicians contacted (1 year),116 number of primary care consultations (1 year),48 (3 years),48 number of referrals (1 year),117 outpatient/Inpatient service use,53 physical distress,52 physical function,55 prescription costs,70 perceived health status,22 presence of mental health disorder,66 primary care consultations (1 year period),105 (3 years),105 primary care experience—self-reported,83 primary healthcare cost,47 primary healthcare use,89 potentially preventable unplanned admission (1-year period),95 quality-adjusted life years,72 73 quality of life,93 98 101 102 self-rated health,118 self-reported falls (12 months),108 symptom burden,101 self-rated Health,64 85 self-perceived health,93 total number of consultation,42 total health care costs42	Functional decline,18 quality of cardiovascular preventive care,27 quality of preventive care27
CCC	Healthcare costs,21 hospital admissions (1 year),21 number of emergency department visits (1 year),21 readmission within 30 days (1 year)21
B=Organ or system-based approaches
Organ systems with CDC	Presence of depressive or anxiety disorder19
CIRS	Disability,17 frailty,17 healthcare utilisation,54 hospitalisation (3 years),18 mortality18	Functional decline18
C=Weighted indices
ACE	Healthcare expenditure23
Cambridge MM Score	Mortality,97 primary care consultation,97 unplanned admission97
CCI	Ambulatory care-sensitive hospitalisations (acute and chronic),106 disability,17 emergency department visits (1 year),21 emergency hospital admission (2 years),119 frailty,17 functional decline (2 years),119 future physical functioning,28 healthcare expenditure,21 hip fractures,103 hospitalisation (1 year),21 64 80 99 109 hospitalisation (3 years),18 mortality (1 year),50 63 99 109 mortality (3 years),18 (5 years),51 63 (10 years),51 63 (15, 20, 25 years),51 number of primary care consultations (3 years),48 number of primary care physician visits (1 year),107 number of specialist visits (1 year),107 potentially preventable unplanned admission (1 year),96 presence of critical illness,46 primary healthcare cost,47 mortality (1 year),57 58 (3 years),48 59 (5 years),58 60 62 (7 years),86 (10 years),28 readmission within 30 days (1 year),21 successful ageing61	Functional decline,18 primary care visits,69 quality of cardiovascular preventive care,27 quality of preventive care27
CLS	Mortality (1 year)57
DBIS	Quality of life98
EI (original and modified)	Hospitalisation (1 year),99 109 mortality (1 year)57 99 109
ERA	Healthcare expenditure,21 mortality (2 years),113 number of days hospitalised (1 year),56 number of emergency department visits (1 year),21 56 number of hospital admissions (1 year),21 56 number of hospital visits (1 year),21 56 nursing home placement (2 years),113 presence of critical illness,46 readmission within 30 days (1 year)21
HCC	Hospitalisation (1 year),21 ED visits (1 year),21 readmission within 30 days (1 year),21 healthcare expenditure (1 year)21
M3 Index	Hospitalisation (1 year),109 mortality (1 year)109
MDMS	Sickness absence episodes taken in 2 years (male)24	Sickness absence episodes taken in 2 years (female)24
MM weighted by ADL scale	Life satisfaction,22 perceived health status22
MM weighted by HUI	Life satisfaction,22 perceived health status22
MM weighted by HUI betas	Life satisfaction,22 perceived health status22
MWI	ADL limitations,121 IADL limitations,121 mortality (10 years),28 cognitive performance,121 future physical functioning,28 125 grip strength,121 health-related quality of life,123 mortality,125 subjective physical functioning,121 suicide mortality123	Gait speed28
QOF (standard)	Mortality (1 year)50
QOF (extended)	Mortality (1 year)50
Severity Burden Score	Mental component score (SF-12)94
D=Other approaches (D-1=Case Mix, D2=Pharmaceutical-based)
ACG	Hospitalisation (1 year),80 mortality (3 years),48 number of primary care consultations (3 years),48 primary healthcare cost,47 readmission within 30 days (1 year)21
ADG	Hospitalisation (1 year),107 number of primary care physician visits (1 year),107 number of specialist visits (1 year)107
CRG	Healthcare expenditure,49 HRQoL using EQ-5D-3L87
Adjusted Morbidity Groups (GMA)	Use of healthcare resources88
HM	Emergency department visits (1 year),21 healthcare expenditure,21 hospitalisation (1 year),21 readmission within 30 days (1 year)21
HSMI	Healthcare cost (primary care)78
Minnesota Tiering	Emergency department visits (1 year),21 114 healthcare expenditure,21 hospitalisation (1 year),21 114 readmission within 30 days (1 year)21
Resource Utilisation Band	Fee-for-service expenditures,77 primary healthcare cost,47 mortality (3 years),48 number of primary care consultations (3 years),48 registered active listing in primary care,100 registered active listing in all healthcare100
CDS	Hospitalisation (1 year),99 mortality (1 year)99
Drug Count	Emergency hospital admission (2 years),120 functional decline (2 years),120 hospitalisation (1 year),99 mortality (1 year),99 (3 years),48 number of primary care consultations (3 years)48
Pra tool Modified using RxRisk-V	Emergency hospital admission (1 year)119
RxRisk-V	Emergency hospital admission (2 years),120 functional decline (2 years)120

ACE-27, Adult Comorbidity Evaluation; ACG, Adjusted Clinical Groups; ADG, Aggregated Diagnosis Groups; ADL, Activities of Daily Living; CCC, Chronic Condition Count; CCI, Charlson Comorbidity Index; CDC, Chronic Disease Count; CDS, Chronic Disease Score; CIRS, Cumulative Illness Rating Scale; CLS, Comorbidity Linked Score; CRG, Clinical Risk Groups; DBIS, Disease Burden Impact Scale; DC, Disease Count; EI, Elixhauser Index; ERA, Elder Risk Assessment; HCC, Hierarchical Condition Categories; HM, Hybrid Model (MN Tier+ERA); HRQoL, health-related quality of life; HSMI, Health Search Morbidity Index; HUI, Health Utility Index; MDMS, Multidimensional Multimorbidity Score; M3 Index, Multimorbidity Measure (M3) Index; MM, Multimorbidity; MWI, Multimorbidity-Weighted Index; Pra tool, Probability of repeated admission risk prediction tool; QOF, Quality and Outcomes Framework; RxRisk-V, A Veterans Association adapted pharmacy-based case-mix instrument; SF-12, Short Form-12.