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Types, Architecture and Hierarchy ofResearch Studies
Abdel-Hamid Serwah, MDProfessor of Internal Medicine
astroenterolo!y"linical #pidemiolo!y $nit, %&M, S"$, #!ypt
'()* - )+*+
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Objectives of the talk
To identify the types and architecture of different study
designs.
To identify the hierarchy of study designs
To Address the applications of each type
To identify the pluses and minuses of each type
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Are All Types of research studies
alie
May any one study type replace
the others
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Some Research Questions?
oes obesity have bad effects on health?
!s "eight reduction beneficial?
!s #$% better than the called traditional learning?
!f you met "ith a strange or ne" phenomenon& ho" do you deal "ith?
'ongenital anomalies and drugs given during pregnancy?
!s the ne" discovered drug better than the available one?
Are smokers at higher risk for (rare cancers) than non smokers?
!s *# carcinogenic?
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Types and *ierarchy of Study esigns
escriptive
'ase report 'ase series Survey
Observational
Analytic
Observational 'orrelational
'ross sectional 'ase+control 'ohort studies
,-perimental Randomied
controlled trials
Strength of evidence for causality between a risk factor and outcome
Other Studies: Systematic review
Meta analysis
Cross over
N of 1 trial
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'ase Series
/hat are they?
Author describes some interesting or intriguing observations
that occurred to a small number of patients
'haracteristics0
escriptive
The simplest design
%ead to hypotheses subse1uently investigated by other types
2'ase+'ontrol& 'ross+Sectional or 'ohort study3
4enerally over short period of time
4enerally no controls
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"ase Series . "ase Reports
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Observational / Analytic Studies
'ross Sectional
'ase+'ontrol
'ohort
,-perimental
5o+o-perimental
Attempt to establish a causal link bet"een a
predictor6risk factor and an outcome.
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Cross-sectional Study'
escriptive value0
*o" many 7niversity students smoke?
/hat is the age and se- distribution and school year of7ni. students "ho smoke?
Analytic value0
!s there an association bet"een regular smoking and test
scores among 7ni. students?
7nivariate
8ultivariate 2controlling for (confounders)3
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'ross+sectional Study0 Advantages
Yields Prevalence (not incidence)
Relatively Fast and Inexpensive - no waitin!
"o loss to #ollow up
Associations can be studied
$ay study several outco%es
&ontrol over %easure%ents
&an be used to assess prora%s (Pre/Post study)
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'ross+sectional study0 isadvantages
Provides only a snaps'ot in ti%e
&annot deter%ine causality
oes not yield incidence
Potential bias in %easurin exposure
&annot study rare outco%es
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Cross-sectional study'Disadvantages
time
- Cannot determine causality
Heart diseases
Smoking
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Measures of association
Disease (Outcome)
Yes No
Risk
Factor(Exposure)
Yes A
No C D
Risk ratio(relative risk)
AA !
CC !D
Risk ratio(relative risk)
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(hat if )are Cases$
Congenital anomalies in relation todrugs given during ppregnancy .
)is* factors of rare cancers#
diseases
Case Control Study
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Structure of "ase "ontrol Studies
DataAnalysis
Outcome!"osure
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Case Selection
+ Case definition
, e.g. lung cancer confirmed by biopsy
ncident cases'
+ )ecruit ne& cases at time of disease occurrence
+ etter for ma*ing inference about associationbet&een ris* factor and developing the disease
Prevalent vs. incident cases
, Prevalent'
+ )is* factors may be more related to survival &ithdisease than development /incidence0 of disease
+ f many people die soon after diagnosis1 may over-represent long term survivors
,
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Selecting Cases /cont.0
!ncident cases are preferable to prevalent cases for
reducing0
recall bias and
over+representation of cases of long duration
The most desirable "ay to obtain cases is to include all
incident cases in a defined population over a specified
period of time
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Selection of 'ontrols0 Sources
The controls should be dra"n from thepopulationof "hich
the cases "ere recruited.
Sampling 9rames for selection of controls0
+ #opulation of an administrative area
- *ospital patients
- Relatives of cases 2spouses : siblings3
- Associates of the cases 2neighbors& co+"orkers& etc3
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Sources of cases and controls in 'ase 'ontrol Studies
Controls Cases
;Sa%ple o# eneral population
;"on-cases in a sa%ple o# t'e
population
;All cases dianosed in t'e
co%%unity
;All cases dianosed in a sa%ple
o# t'e population
;Sa%ple o# patients in all
'ospitals w'o do not 'ave
t'e disease
;Sa%ple o# patients in t'e sa%e
'ospital w'o do not 'ave t'e
disease
;All cases dianosed in all
'ospitals (or in sinle *)
;Spouses+ siblins or associates
o# cases
;Any o# t'e above %et'ods
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#atients0 Sources of !nformation on ,-posure
Sources of information on e2posure'
Patients
parents' in children or severe illness.
)elatives1
Hospital records1 3mployment records1 etc.
(hen information is obtained via
intervie&s1 recall bias is often a concern.
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Measure of Association in "ase"ontrol Studies
DataAnalysis
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8easures of association in case control
Studies
Disease Status
Case Control
Exposure
Yes A
No C D
Odds ratio
A ,
. , &
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Odds Ratio 2OR3
A ratio t'at %easures t'e c'ance or lieli'ood o#
exposure#or cases co%pared to controls
Odds o# exposure0 nu%ber exposed nu%ber
unexposed
OR "u%erator1 Odds o# exposure #or cases OR eno%inator1 Odds o# exposure #or controls
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2334335otal
44266"on-s%oer
789774S%oer:xposure
Status
"o &*
(&ontrols)
&* cases
(&ases)
isease Status
,-amples0 'alculating the Odds Ratio
Odds Ratio 0 0A
.&
774 x 442
789 x 66
0 794
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!nterpreting the Odds Ratio
5'e odds o# exposure #or cases are 794 ti%es t'e
odds o# exposure #or controls
5'ose wit' &* are 794 ti%es%ore liely to be
s%oers t'an t'ose wit'out &*
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433433
5otal
77323"o Alco'ol
;3793Alco'ol:xposure
Status
"o &ancer&ancer
isease Status
Alcohol 'onsumption and %aryngeal 'ancer
Odds Ratio 0 0A
.&
793 x 773
;3 x 23
0 26;
The odds of alcohol consumption are times greater among
those "ith laryngeal cancer than among those "ithout cancer.
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OR"# OR$# OR%#
Odds o#exposure#or cases arereatert'an
t'e odds o#exposure #orcontrols
Odds o#exposure aree
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ORs& #+alues and >@ '!s for 'ase+'ontrol Study"ith B ifferent Sample Sies
Sample Si&e
Para%eter&o%puted n043 n0>3 n0>33
OR C.D C.D C.D
p-value D.@DD D.CDD D.DDE
;>? &Is D.@+F.F D.>+
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Strent's o# t'e &ase-&ontrol Study
8ost efficient design for rare diseases
!t shortens the "aiting time re1uired by cohort studies
'an be used "hen R'T is not logistically or ethicallyfeasible.
,fficient& 1uick and easy& cost effective& fe"er practicalrestrictions
Re1uires a smaller study population than a cohort study
'an establishes an association 2Odds Ratio3
7seful for generating hypotheses 2multiple risk factors canbe e-plored3.
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'an not prove causality because of0
7ncertainty of e-posure+disease time relationship
The e-istence of confounding factors
5ot efficient for studying rare e-posures
Subject to biases 2recall : selection bias&
misclassification3
isadvantages of 'ase+'ontrol Studies
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Correlation and
)egression
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Correlation and )egression
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"orrelation
What type of relationship eists !et"een the t"o
#aria!les and is the $orrelation si%nifi$ant&
x y
'i%arettes s(o)ed per day
*$ore on *+,
-ei%ht
-o.rs of ,rainin%
/planatory
01ndependent2 3aria!le
Response
04ependent2 3aria!le
+ 5.antitati#e relationship !et"een t"o inter#al or ratio
le#el #aria!les
6.(!er of +$$idents
*hoe *i7e -ei%ht
8.n% 'apa$ity
9rade :oint +#era%e
1;
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"orrelation
Measures and describes the stren!th anddirection of the relationship
/i0ariate techni1ues re1uires two 0ariablescores from the same indi0iduals 2dependent
and independent 0ariables3 Multi0ariate when more than two
independent 0ariables 2e4! effect ofad0ertisin! and prices on sales3
5ariables must be ratio or inter0al scale
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Negative Correlationasxincreases, y
decreases
x= hours of training (horizontal axis)
y= number of accidents (vertical axis)
Scatter Plots and !ypes of Correlation
=
?=@=
A=
B=
=
= A ? < C B= BA B? B< BC A=
-o.rs of ,rainin%
+$$idents
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Positive Correlationasxincreases,y increases
x= !" scorey= #P!
#P!
Scatter Plots and !ypes of Correlation
$%&&'%'%&
'%&&*%*%&*%**%&&
+%&
+%
'%*
'&& '& $&& $& && & && & && & &&
.ath !"
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No linear correlation
x= height y= /0
Scatter Plots and !ypes of Correlation
+&
+&
+$&
+'&+*&
++&
+&&
1&
&& $ * &
-ei%ht
1;
Scatte #lots and $ "es of
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Strong' negatie relationsip
*ut non-linear+
Scatter #lots and $y"es ofCorrelation
Correlation Coefficient r
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Correlation Coefficient r
! measure of the strength and direction of a linear
relationshi2 bet3een t3o variables
"he range of ris from + to +%
/f ris close to +
there is a strong2ositive
correlation%
/f ris close to + there
is a strong negativecorrelation%
/f ris close to &
there is no linear
correlation%
+ & +
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&utliers44444
Outliers are dangerous
Here ,e ae a spuriouscorrelation o r$./01
,itout 23' r$./41
,itout 23 5 6E'r$./7#
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The correlation coefficient of number of times absentand final !rade is r6 7(489:4 The coefficient ofdetermination is r' 6 27(489:3' 6 (48:(;4
Interpretation< About 8:= of the 0ariation in final !radescan be e>plained by the number of times a student isabsent4 The other := is une>plained and can be due tosamplin! error or other 0ariables such as intelli!ence,amount of time studied, etc4
Strengt o te Association
The coefficient of determination, r', measures
the stren!th of the association and is the ratioof e>plained 0ariation in yto the total 0ariationin y4
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Cohort study
"on-32perimental32perimental
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Prospective1 longitudinal1 follo& upStudies' Cohort
A cohort study is a0
'omparative
Observational6 analytic studySubjects are grouped by their e-posure status
All subjects& are follo"ed for"ard in time to determine
if one or more ne" outcomes 2diseases3 occur
The rates of disease incidenceamong the e-posedand
une-posed groups are determined and compared.
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Architecture of 'ohort studies
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,lements of a cohort study
Selection of sample from population
8easures predictor variables in sample
9ollo" population for period of time
8easure outcome variable
Famous cohort studies
9ramingham
5ursesH *ealth Study 25*S3
/omen health !nitiative 2/*!3
#hysiciansH *ealth Study
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"ohort studies< Marchin! towards outcomes
Lancet*&&*4@>DE'$+-$
"he defining characteristic of all cohort studies is that the5 trac6 2eo2le for3ard in
time fro( epos.re to o.t$o(e% 7ata collection ma5 be 2ros2ective orretros2ective% /F 'ontra$epti#es and 43,%
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"ohort studies< marchin! towards outcomes
/posed s.!Ge$ts
Hneposed s.!Ge$ts
'lassi$ 0'on$.rrent2
'ohort *t.dy4isease
4isease
,oday I >J >J B= I B=
-istori$al
06onJ$on$.rrent2
'ohort *t.dy
/posed s.!Ge$ts
Hneposed s.!Ge$ts
4isease
4isease
"ime in 8ears
,oday I >J >J B= I B=
"ime in 8ears
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Cohort Study' Design 4utlines
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:xperi%ental Studies1 &ontrolled trials
,-perimental drug or procedure compared
"ith another& "ith a placebo& or "ith thestandard procedure.
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Structure o# R&5 Studies
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,-amples of 'ohortStudies
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Schematic 4utline of StudyDesign
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)C!' )esearch 5uestion
%s Mass treatment of sc&isto' more effective t&an
treatment of "ositive cases after stool analysis
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Mass !reatment 6s. Stool analysis and treatmentof 7ve Cases
Study #o"ulation
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5urseHs *ealth Study 25*S3
5one-perimental esign
Individuals classified according to "hether they
received *ormonal Replacement Therapy 2*RT3& or
notSubjects "ere follo"ed for various health outcomes0
heart attacks
strokes
breast cancer and so on.
Exampleof publication0 Stampfer& 8.& 'oldit& 4.& /illett& /.& 8anson& I.& Rosner& $.& Speier& 9.& et al. 2E>>E3.#ostmenopausal estrogen therapy and cardiovascular disease. Ten+year follo"+up from the nursesJ health study.NewEngland Journal of Medicine, 3252EE3& F@G+FGC.
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5urseHs *ealth Study 25*S3 5on+
e-perimental esign
8Healt outcomes8 eart attacks' strokes' *reast cancer and so on/
/omenHs *ealth !nitiative 2/*!30 ,-perimental esign
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/omenHs *ealth !nitiative 2/*!30 ,-perimental esign
!he (H study randomly assigned about half its sub9ectsto'
- Group :' that received hormone replacementtherapy/H)!0.
- Group ;. received an identical loo*ing placebo.
%ll Sub9ects &ere follo&ed for
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/omenHs *ealth !nitiative 2/*!3
,-perimental esign 2R'T3
Healt outcomes8 eart attacks' strokes' *reast cancer and so on/
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'omparison of /*! and 5*S
$oth analyed relationships bet"een *RT 2e-planatory
variable3 and various health outcomes 2response
variables3
/*!investigators assigned the e-posure 2*RT3
e-perimental
5*Sinvestigators measured the e-posure but did not assign it
non+e-perimental 2observational3
,ff t f 5i ti ti f S ki
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,ffect of 5icotine on cessation of Smoking
Source:JAMA 1994;271:595-600 32planatory variable' "icotine or placebo patch
?@ sub9ects /A@ in each group0
)esponse variable # outcome' Cessation of
smo*ing /yes#no0
RandomAssignment
4roup E
BD smokers
Treatment E
5icotine #atch
4roup C
BD smokers
Treatment C
#lacebo #atch
Yes
No
Yes
No
http://jama.ama-assn.org/cgi/content/abstract/271/8/595http://jama.ama-assn.org/cgi/content/abstract/271/8/595 -
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%nalysis of )C!
%nalyBed li*e cohort study &ith ))
ntention to treat analysis !!
Most conservative interpretation
nclude all persons assigned tointervention group /including those &hodid not get treatment or dropped out0
Subgroup analysis Groups identified pre-randomiBation
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Keas.res of Ris) in 0$ohort *t.dy2
Response to treat(ent
treat(ent R B
Les 6o
R A
a !
$ d
a I $ ! I d
a I !
$ I d
response ratea
a I !M
$
$ I d
a
Relati#e ris)Ea I !
$
$ I d
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,thics of ,-perimental Studies
,1uipoise + balanced doubtK canHt intentionallye-pose subjects to harm or "ithhold benefit
!nformed consent0 subjects must be a"are of study
objectives $eneficence0 must provide overall benefit to society
5on+malefficience 2onHt do harm3
Take care0 donHt deprive patients from kno"neffective treatment
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Strengths of cohort studies
Some evidence of causality.Lno" that predictor variable"as present before outcome variable occurred
irectly measure incidenceof a disease outcome
'an study multiple outcomes of a single e-posure 2RR ismeasure of association3
Smoking
' 'a lung
'a esophagus
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/eaknesses of cohort studies
,-pensive
!nefficient for studying rare outcomes
'ong. Anomalies and drug during pregnancy
'a pancreas and smoking
Often need long follo"+up period or a very large population
'AR!A
%oss to follo"+up& cross over can affect validity of findings
9ramingham
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Problems &ith cohort studies
Selection 2patients6control3 bias
Attrition 2rop out3
'o intervention
'ross over 8isclassification bias
'onfounders
!nformation bias
Recall bias
!ntervie"ers
#ublication bias
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*o" to guard against and deal "ith problems?
!horough identification of cases andcontrols
)andomiBation in )C!s
lindness in )C!s
Ese intention to treat analysis !!
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Temporal direction of study desi!ns
Lancet **+ 9:;8 ,-./1
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4ther Study !ypes
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Systematic Re0iews .Meta-
analyses
St d P id
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Study Pyramid
9est
Worst
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0rimes DA and Sc&ul 23 **' An overview of clinical researc&' 4ancet 5,67,-./1'
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3pidemiologic study designs
?hat type of study to chose depends onposure 2Study factors3
- Identify outcome factors 20ariables3
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#>ercise @)
Cryptosporidiosis is an enteric illness that isfreFuently &aterborne.
hala*dina and colleagues /;@@A0 could find nopublished studies of the ris* factors for
cryptosporidiosis in immunocompetent adults.
Patients &ith cryptosporidiosis &ere recruited from asurveillance system1 and age-matched controls &ererecruited by random-digit dialing.
Sub9ects in both groups &ere intervie&ed bytelephone to obtain information about previouse2posures
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Calvert EL, Hou!to" LA, Coo#er $, et al% Lo"-ter&
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, , # , 'rove&e"t '" (u"ct'o"al )y*#e#*'a u*'"
!y#"ot!era#y% +a*troe"teroloy 2002; 12: 177-5%
%CG)4E"D %MS' (e have sho&n hypnotherapy /H!0 tobe effective in irritable bo&el syndrome1 &ith long-termimprovements in symptomatology and Fuality of life /54I0.
!his study aimed to assess the efficacy of H! in functionaldyspepsia /JD0.
M3!H4DS' % total of :;? JD patients &ere randomiBed to H!1supportive therapy plus placebo medication1 or medicaltreatment for :? &ee*s.
Percentage change in symptomatology from baseline &asassessed after the :?-&ee* treatment phase /short-term0 and
after =? &ee*s /long-term0 &ith ;? H!1 ;K supportive therapy1and ;L medical treatment patients completing all phases ofthe study. 54I &as measured as a secondary outcome.
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(hat is the Study Design$
.!o&a* SH, S'le" /% E((ect o" )'a"o*t'c e(('c'e"cy o(
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, ya"ale*'a (or u")'((ere"t'ate) a)o&'"al #a'"% r J
Sur 200; 90:5-9%
!he Fuestion of &hether it is safe to provide analgesia forpatients &ith undifferentiated acute abdominal pain is mar*edby longstanding controversy over the possible mas*ing ofphysical findings.
!he goal of this revie& is to assess the pertinent studies.
% Medline search &as performed in %pril ;@@;1 using the termsanalgesia1 abdominal pain1 acute abdomen and morphine.
4ther articles &ere identified using the bibliographies of papersfound through Medline.
%ll articles reporting clinical trials of analgesia and its effects on
diagnosis or physical e2amination &ere revie&ed.
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% revie& that is conductedaccording to clearly stated1 scientificresearch methods1 and is designed to
minimiBe biases and errors inherentto traditional1 narrative revie&s.
Margaliot1 Nvi1 evin C. Chung. Systematic )evie&s' % Primer for Plastic Surgery)esearch. P)S Oournal. :;@# /;@@0
(hat is a Systematic )evie&$
(hat is the significance of
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(hat is the significance ofSystematic )evie&s$
!he large amount of medical literature reFuires clinicians
and researchers ali*e to rely on systematic revie&s in
order to ma*e an informed decision.
Systematic )evie&s minimiBe bias. % systematic revie&
is a more scientific method of summariBing literature
because specific protocols are used to determine &hich
studies &ill be included in the revie&.
evin C. Chung1 MD1 Patricia . urns1 MPH1 H. Myra im1 ScD1 Clinical Perspective' % Practical Guide to Meta-%nalysis. !he Oournal
of Hand Surgery. 6ol. A:% "o.:@ December ;@@?. p.:?:
M t % l i
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Meta- %nalysis
Meta-analysis is a statisticaltechniFue for combining the resultsof independent1 but similar1 studies
to obtain an overall estimate oftreatment effect.
Margaliot1 Nvi1 evin C. Chung. Systematic )evie&s' % Primer for Plastic Surgery)esearch. P)S Oournal. :;@# /;@@0 p.:QK@
M t % l i / t 0
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Meta- %nalysis /cont.0
(hile all meta-analyses are based onsystematic revie& of literature1 not allsystematic revie&s necessarily include
meta-analysis.
Margaliot1 Nvi1 evin C. Chung. Systematic )evie&s' %
Primer for Plastic Surgery )esearch. P)S Oournal. :;@# /;@@0p.:QK@
Junnel Plot
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u e o
8A funnel "lot is used as a way to assess "u9lication9ias in meta.analysis':
% Jorest Plot
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% Jorest Plot