Cluster Randomised Trials Guide_Feb2010_0

8/16/2019 Cluster Randomised Trials Guide_Feb2010_0

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COCHRANE INFECTIOUS D ISEASES GROUPcidg.cochrane.org

Data collection, analyi andre!orting"

A g#ide to incl#ding cl#ter rando$i%edtrial and !artici!ant rando$i%ed trial ininter&ention re&ie'

About the guide: The Cochrane In(ectio# Dieae Gro#! )CIDG* ha de&ied thi

g#ide"

+. To hel! re&ie' a#thor identi(y cl#ter rando$i%ed controlled trial )RCT*

-. To o#tline the analyi and re!orting $ethod that $#t e e$!loyed 'hen

cl#ter rando$i%ed trial are incl#ded in a Cochrane re&ie'/. To !ro&ide a 'or0ed e1a$!le o( ho' a re&ie' a#thor can in&etigate the e2ect

o( cl#tering #ing eniti&ity analyi 'hen the trial3 analyi did not $a0e an

ad4#t$ent (or the e2ect o( cl#tering.

The $ethod decried in thi g#ide are rele&ant (or re&ie' that incl#de cl#ter RCT

or thoe that incl#de RCT rando$i%ed y indi&id#al !artici!ant and cl#ter RCT. The

data collection and analyi content chec0lit ha een integrated into thi doc#$ent

and there(ore yo# can diregard the chec0lit. Thi g#ide ho#ld e #ed alongide the

CIDG !re5#$iion chec0lit (or the !rotocol and re&ie' )a&ailale on the CIDG

'eite*. 6hile the !re5#$iion chec0lit ho#ld e e$ailed to the Re&ie' Gro#!Co5ordinator 'hen the !rotocol i #$itted (or editorial and !eer re&ie', it i not

$andatory to end the co$!leted &erion o( thi g#ide.

1. What is a cluster randomized trial?Generally the #nit o( rando$i%ation o( a RCT i the indi&id#al !artici!ant )i.e. !atient*

and there(ore #ch trial are ter$ed RCT. Ho'e&er, occaionally the #nit o(

rando$i%ation o( a RCT i the cl#ter )e.g. ho#ehold, chool, &illage or co$!o#nd*. In

other 'ord, cl#ter o( !atient are allocated to the inter&ention ar$ o( the trial

#ing a rando$ly generated allocation e7#ence, rather than allocating eachindi&id#al !atient to inter&ention ar$ in t#rn. Trial (or 'hich the #nit o(

rando$i%ation i the cl#ter are o$eti$e, #t not al'ay, called cl#ter rando$i%ed

trial in trial article. See Cochrane Handoo0+ ection +8./.+ (or (#rther detail.

+ Higgin 9PT, Green S )editor*. Cochrane Handbook for Systematic Reviews of Interventions :.;.; . '''.cochrane5handoo0.org.

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2. Analysis and reporting methodsCl#ter RCT ho#ld not e re!orted and analy%ed in the a$e 'ay a (or RCT

rando$i%ed y the indi&id#al. The $ethod decried in thi g#ide are rele&ant (or

re&ie' that incl#de cl#ter RCT or thoe that incl#de RCT rando$i%ed y indi&id#al!artici!ant and cl#ter RCT.

2a. Data collection and analysis methods There are e&eral ection in the ?Data collection and analyi3 $ethod ection.

@e(ore 'riting the te1t, re(er to the !ecic ection o( Cochrane Handoo0 noted at

the tart o( each ection. A(ter reading the Cochrane Handoo0 ection, 'rite a

entence or t'o ao#t ho' yo# 'ill addre each chec0lit 7#etion.

For e1a$!le, the rt chec0lit 7#etion i" B6ill yo# inde!endently creen the

earch re#lt (or !otentially rele&ant trial The corre!onding te1t (or the?Selection o( t#die3 #heading co#ld e" BSarah Donegan and Pa#l Garner 'ill

inde!endently creen the earch re#lt (or !otentially rele&ant trial.

Methods in the protocol: The $ethod ho#ld e !re!ared in the (#t#re tene )eg

B'e 'ill analye*. Re$e$er to acti&ate thoe #heading )eg ?Selection o(

t#die3* a!!ro!riate (or the !ecic Cochrane Re&ie'.

Methods in the revie: Change the $ethod to the !at tene )eg B'e

analyed*. The $ethod ho#ld not e #tantially di2erent to thoe in the

!rotocol, and no re#lt ho#ld e re!orted in thi ection )eg regarding the !reence

o( heterogeneity or n#$er o( trial*. A tated in the Cochrane Handoo0, i( Ba re&ie'i #nale to i$!le$ent all o( the $ethod o#tlined in the !rotocol, it i reco$$ended

that the $ethod that 'ere not i$!le$ented e o#tlined in the ection headed

?Di2erence et'een !rotocol and re&ie'3, o that it er&e a a !rotocol (or (#t#re

#!date o( the re&ie'.

!election o" studiesRead section 7.2 of the Cochrane Handbook: Selecting studies.

6ill yo# inde!endently creen the earch re#lt (or !otentially rele&ant trial

6ill yo# retrie&e the corre!onding (#ll article

6ill yo# ae eligiility #ing an eligiility (or$

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6ho 'ill ae eligiility

6ill yo# ae eligiility inde!endently (ro$ each other

6ill yo# 'rite to the trial a#thor regarding eligiility i( eligiility i #nclear

Ho' 'ill yo# reol&e dicre!ancie et'een the eligiility re#lt o( the re&ie' a#thor

6ill each o( the trial re!ort e cr#tini%ed to en#re that $#lti!le !#lication (ro$ thea$e trial are incl#ded only once

6ill yo# lit the e1cl#ded t#die and the reaon (or their e1cl#ion

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Data e$traction and management There are t'o ty!e o( in(or$ation to incl#de in thi ection, one aro#nd general data

e1traction !rocee and the other ao#t the ty!e o( data to e e1tracted.

Read sections 7. to 7.! of the Cochrane Handbook: "hat data to collect#Sources of data# $ata collection forms# %&tracting data from re'orts# %&tracting

study results and converting to the desired format# and (anaging data.

About the general data e$traction process

6ho 'ill e1tract data

6ill yo# inde!endently e1tract data

6ill yo# #e data e1traction (or$

6ill yo# !re5!ilot the (or$

Ho' 'ill yo# reol&e any di2erence in the data e1traction6ill yo# contact the !#lication a#thor in the cae o( #nclear or $iing data

About the type o" data to be e$tracted

I( t#die o( di2erent deign )e.g. RCT rando$i%ed y indi&id#al and RCT

rando$i%ed y cl#ter* are incl#ded in the re&ie', the ty!e o( data that need to e

e1tracted 'ill e di2erent (or each deign. In thi cae, inert heading in thi ection

?RCT rando$i%ed y indi&id#al3 and ?RCT rando$i%ed y cl#ter3 to clari(y the

ditinction.

@e(ore 'riting thi ection, decide 'hich ty!e o( o#tco$e data are !otentially

rele&ant to yo#r re&ie' and do not decrie data e1traction (or irrele&ant o#tco$e.

Refer to section ).2.* of the Cochrane Handbook: +y'es of data.

%he type o" data to be e$tracted "or &'%s randomized by individual

6ill yo# e1tract the n#$er rando$i%ed and the n#$er analy%ed in each treat$entgro#!, (or each o#tco$e

6hat data 'ill yo# e1tract (or dichoto$o# o#tco$e (or RCT rando$i%ed y indi&id#al*. ,or e&am'le- the number of 'artici'ants e&'eriencing the event and the number of

'artici'ants in each treatment grou' Refer to section 7.7.2 of the CochraneHandbook: $ata e&traction for dichotomous outcomes.

6hat data 'ill yo# e1tract (or contin#o# o#tco$e (or RCT rando$i%ed y indi&id#al2. ,or e&am'le- arithmetic means and standard deviations for each treatment grou'

together with the numbers of 'artici'ants in each grou'. If the data have beenre'orted using geometric means- record this information and e&tract a standarderror on the log scale. If medians have been used- e&tract medians and aim to alsoe&tract ranges. Refer to section 7.7. of the Cochrane Handbook: $ata e&tractionfor continuous outcomes.

6hat data 'ill yo# e1tract (or co#nt data o#tco$e (or RCT rando$i%ed y indi&id#al. ,or e&am'le- e&tract the number of events in the treatment and control grou' and

the total 'erson time at risk in each grou' or the rate ratio and a measure of

variance /e.g. standard error0 directly from the trial re'ort. Refer to section 7.7.1 ofthe Cochrane Handbook: $ata e&traction for counts.

6hat data 'ill yo# e1tract (or ti$e to e&ent data o#tco$e (or RCT rando$i%ed y

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indi&id#al. ,or e&am'le- e&tract the ha3ard ratio and a measure of variance directly from the

trial re'ort. Refer to section 7.7.4 of the Cochrane Handbook: $ata e&traction fortime5to5event outcomes.

%he type o" data to be e$tracted "or &'%s randomized by cluster

6ill yo# e1tract the n#$er rando$i%ed and the n#$er analy%ed in each treat$entgro#!, (or each o#tco$e

6hat data 'ill yo# e1tract (or cl#ter RCT that ad4#t (or cl#tering in the analyi1. ,or e&am'le- the measure of e6ect /such as risk ratio- odds ratio or mean

di6erence0 and a condence interval or measure of variation- such as a standarderror. +ake care to ensure that the correct data is e&traction because often clusterad8usted results and non5ad8usted results are re'orted in trial articles. See section*4.. of the Cochrane Handbook: (ethods of analysis for cluster5randomi3ed trials.

6hat data 'ill yo# e1tract (or cl#ter RCT that do not ad4#t (or cl#tering in the analyi4. ,or e&am'le- the same data as described above for RC+s randomi3ed by individual.

In additional an estimate of the average cluster si3e /or number of 'atients andnumber of clusters0 and the intra5cluster correlation coe9cient should bee&tracted. See section *4.. and *4..4 of the Cochrane Handbook: ''ro&imateanalyses of cluster5randomi3ed trials for a meta5analysis: e6ective sam'le si3es#and ''ro&imate analyses of cluster5randomi3ed trials for a meta5analysis: in;atingstandard errors.

Assessment o" ris) o" bias in included studiesRead section ! and *4..2 of the Cochrane Handbook: ssessing risk of bias in

included studies# and ssessing risk of bias in cluster5randomi3ed trials.

6ho aeed ri0 o( ia

6a ri0 o( ia aeed inde!endently

6ill yo# #e an ae$ent (or$

6ill yo# atte$!t to contact the a#thor (or any in(or$ation not !ecied or #nclear

Ho' 'ill yo# reol&e any diagree$ent

6hich co$!onent 'ill yo# ae7. the numberrandomi3ed0 and any other relevant information. ,or selective outcome re'orting- you could state any discre'ancies between the methods and the results in terms of the outcomes measured and the outcomes re'orted# or identify any outcome that you know would have been measured but was not re'orted in the 'ublication. ,orother biases: describe any other trial features that you think could a6ect the trial?s

results /e.g. trial sto''ed early- no sam'le si3e calculation etc0. dditionally-descri'tions need to be given for the com'onents relevant for cluster randomi3edtrials.

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6ill yo# aign 4#dg$ent concerning the ri0 o( ia (or each co$!onent Ho'). ,or e&am'le- 8udgments are classied as @yesA- @noA or @unclearA indicating a low-

high- or unclear>unknown risk of bias res'ectively.

6ill yo# gro#! the o#tco$e in the ae$ent*B. +he Cochrane Handbook states that one 8udgment should be assigned for each

study for se=uence generation- allocation concealment- selective outcomere'orting- and other biases. ,or blinding and incom'lete outcome data- one 8udgment 'er outcome in the trial chould be assigned. lternatively- if there aremany outcomes- you could grou' the secondary outcomes and assess themtogether as described in the Cochrane Handbook.

Ho' 'ill yo# record the re#lt**. +here are two useful summary gra'hs which are easy to dis'lay and save: risk of

bias summary? and risk of bias gra'h# in addition to the risk of bias tables.

Measures o" treatment e*ectRead sections ).* and ).2 of the Cochrane Handbook: Introduction to analysing

data and undertaking meta5analysis# and +y'es of data and e6ect measures.In thi ection decrie the $ea#re o( e2ect that 'ill e #ed (or each ty!e o(

o#tco$e that yo# decided 'a !otentially rele&ant 'hen 'riting the $ata e&traction

and (anagement ection.

6hat $ea#re o( e2ect 'ill yo# #e to co$!are dichoto$o# data*2. +he risk ratio is recommended generally- although in some case the odds ratio or

risk di6erence is more a''ro'riate. Refer to sections ).2.2 and ).. of theCochrane Handbook: %6ect measures for dichotomous outcomes# and (eta5analysis of dichotomous outcomes.

6hat $ea#re o( e2ect 'ill yo# #e to co$!are contin#o# data

*. If continuous data are summari3ed by arithmetic means and standard deviations- 'resent the mean di6erences. "here continuous data are summari3ed usinggeometric means- re'ort geometric mean ratios. (edians and ranges should bere'orted in a table. See sections ).2. and )..1 of the Cochrane Handbook: %6ectmeasures for continuous outcomes# and (eta5analysis of continuous outcomes

6hat $ea#re o( e2ect 'ill yo# #e to co$!are co#nt data*. Rate ratios are often used to combine count data. Rate ratios can be calculated

manually if they are not re'orted in the trial re'orts. Refer to sections ).2.1 and)..! of the Cochrane Handbook: %6ect measures for counts and rates# and (eta5analysis of counts and rates.

6hat $ea#re o( e2ect 'ill yo# #e to co$!are ti$e to e&ent data*1. Ha3ard ratios are used to com'are time to event data. Refer to sections ).2.4 and

)..) of the Cochrane Handbook: %6ect measures for time5to5event /survival0outcomes# and (eta5analysis of time5to5event outcomes.

6ill all re#lt e !reented 'ith : condence inter&al

+nit o" analysis issuesRead section ). and *4. of the Cochrane Handbook: Study designs and

identifying the unit of analysis# and Cluster5randomi3ed trials.

I( yo# antici!ate that trial 'ill e $#lti5ar$ed, ho' 'ill yo# acco#nt (or thi in theanalyi

*4.


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analysis- how will you account for this in your analysis

,or e&am'le- when the analyses have not ad8usted for clustering- attem'ts can be madeto ad8ust the results for clustering- by multi'lying the standard errors of the estimates bythe s=uare root of the design e6ect where the design e6ect is calculated as *D/m5*0EICC.+his re=uires information to be re'orted i.e. the average cluster si3e /m0 and the intra5cluster correlation coe9cient /ICC0. %=uivalently- to ad8ust for clustering- an e6ectivesam'le si3e can be calculated by dividing the original sam'le si3e divided by a =uantitycalled the design e6ect. ,or dichotomous data both the number of 'artici'ants and thenumber e&'eriencing the event should be divided by the same design e6ect and thenumbers are rounded to whole numbers. See sections *4..- *4..1 and *4..4 of theCochrane handbook: ''ro&imate analyses of cluster5randomi3ed trials for a meta5analysis: e6ective sam'le si3es# %&am'le of incor'orating a cluster5randomi3ed trial# and ''ro&imate analyses of cluster5randomi3ed trials for a meta5analysis: in;ating standarderrors.

,urthermore- if the ICC is unknown it can be estimated from e&ternal sources- such astrials with similar cluster si3es and features. If the similar trials do not re'ort the ICC

e&'licitly- it may be estimated using an a''ro&imation. If the standard error ad8usted forclustering /d8usted S%0- the standard error that is not ad8usted for clustering /S%0- and theaverage cluster si3e /m0 can be obtained from the similar trial- then an a''ro&imation ofthe ICC would be given by:

+he methods described above can then be a''lied using the a''ro&imate ICC to ad8ust the

trial for clustering. However- when using e&ternal sources- such as similar trials- to

estimate the ICC for a trial that did not ad8ust for clustering- it is im'ortant that

sensitivity analyses are carried out by e&cluding the trial that did not originally

ad8ust for clustering to see if the results of the meta5analysis change.

If no similar trials e&ist then a di6erent sensitivity analysis could be carried out using arange of estimates for the ICC to see if clustering could in;uence the individual trial?sresult. +his method is e&'lained in section of this guide.

Dealing ith missing dataRead sections *4.* and *4.2 of the Cochrane Handbook: (issing data# and

Intention5to5treat issues.

I( there i $iing data 'hat ty!e o( analyi 'ill yo# a!!ly e.g. co$!lete cae, intention totreat

*7. com'lete5case analysis is generally recommended if there are missing data.

6hat ty!e o( analyi 'ill yo# carry o#t i( there i no $iing data*!. im to carry out analyses according to the intention5to5treat 'rinci'le if there are no

missing data.

Assessment o" heterogeneityRead section ).1 of the Cochrane Handbook: Heterogeneity.

Ho' 'ill yo# ae heterogeneity Ho' 'ill yo# deter$ine there i tatitically ignicantheterogeneity*). Fne a''roach is to ins'ect the forest 'lots to detect overla''ing condence

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!ubgroup analysis and investigation o" heterogeneityRead section ).4 and *4..7 of the Cochrane Handbook: Investigating

heterogeneity# and Issues in the incor'oration of cluster5randomi3ed trials.

6ill yo# in&etigate heterogeneity #ing #gro#! analye

Pro&iding there are #cient trial, 'ill yo# in&etigate heterogeneity #ing $eta5regreion

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2b. &eporting There are e&eral ection in the re&ie' 'ere additional in(or$ation i re7#ired (or

cl#ter rando$ied trial. The (ollo'ing note can e #ed a a chec0lit 'hile 'riting

the re&ie' and analying the data.

Abstract

Re!ort the n#$er o( cl#ter RCT incl#ded in the re&ie' in addition to re!orting the

n#$er o( t#die incl#ded 'ith other deign.

'riteria "or considering studies "or this revie: %ypes o"

studies

Jention that RCT (or 'hich the #nit o( rando$i%ation i the cl#ter )e.g. ho#ehold* areincl#ded in addition to decriing other ty!e o( t#die that are eligile (or incl#ion.

Re!ort 'hether RCT 'ith only t'o cl#ter 'ill e e1cl#ded.

&esults: 'haracteristics o" included studies For e&ery cl#ter RCT re!ort the (ollo'ing detail in the $ethod ro' o( the tale"

Identi(y the trial a a cl#ter RCT, (or e1a$!le, ?St#dy deign" cl#ter rando$i%ed trial3.

The #nit o( rando$i%ation, #ch a ?Unit o( rando$i%ation" claroo$3.

6hether the trial ad4#ted (or cl#tering in the analyi, #ch a ?Ad4#ted analye (orcl#tering" ye3.

Re!ort the $ethod to ad4#t (or cl#tering, #ch a ?Ad4#t$ent $ethod" $#lti5le&el

$odel3.

I( otained, re!ort the intra5cl#ter correlation coecient (or each o#tco$e o( interet#ch a ?ICC" ;.;-3.

Re!ort the n#$er o( cl#ter and n#$er o( !atient, #ch a, ?N#$er o( cl#ter" +;n#$er o( !atient" /:- 3.

Re!ort the a&erage cl#ter i%e, #ch a, ?A&erage cl#ter i%e" /- 3.

Any !ecic deign (eat#re, in !artic#lar, $atching or tratication, #ch a, 3Feat#re"Jatched y location3.

&esults: Description o" studies State the n#$er o( cl#ter rando$i%ed trial and !ro&ide a lin0 to the t#dy re(erence toidenti(y the cl#ter rando$i%ed trial.

Pro&ide a #$$ary o( the detail decried in the $ethod ro' o( the characteritic o(incl#ded t#die (or all t#die. In !artic#lar, decrie the n#$er o( trial that ad4#tedthe analye (or cl#tering and re(erence thee t#die.

&esults: &is) o" biasIn the ri0 o( ia tale ae the additional co$!onent a decried in the $ethodection y adding ite$ to the ri0 o( ia tale in the !ro!ertie o1 o( Re&ie' Janager.

In the ri0 o( ia te1t !ro&ide a #$$ary o( the re#lt o( the ri0 o( ia tale (or allco$!onent (or all trial.

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&esults: Data and analyses The re#lt o( cl#ter RCT that are not ad4#ted (or cl#tering ho#ld e !reented in atale. The re#lt o( RCT that are not ad4#ted (or cl#tering ho#ld e not co$ined #ing$eta5analyi or !reented in (oret !lot.

Re#lt o( cl#ter RCT that ha&e not ad4#ted (or cl#tering ho#ld not e !reented inthe a$e tale a thoe that did ad4#t (or cl#tering or trial rando$i%ed y indi&id#al.

6hen re#lt (ro$ cl#ter RCT are !reented in a tale or (oret !lot, clearly tate'hether the re#lt did ad4#ted (or cl#tering #ing a (ootnote, title or decri!tion in there&ie' te1t.

6hen the #nit o( rando$i%ation (or cl#ter RCT &arie, (or e1a$!le, o$e trialrando$i%ed y chool and other trial rando$i%ed y claroo$ etc, clearly tate the #nito( rando$i%ation 'ith the trial3 re#lt.

&esults: *ects o" interventions

6hen decriing the re#lt o( a cl#ter RCT $a0e #re it i clear that the trial ad4#ted

)or did not ad4#t* (or cl#tering.

6hen inter!reting the re#lt o( cl#ter RCT conideration ho#ld e gi&en to the #nit o(analyi to a&oid $iinter!retation.

• ,or e&am'le- if the analysis is 'erformed using a summary statistic from each cluster-

the analyses are said to be 'erformed at the cluster level and results should beinter'reted at the cluster level rather than for individual 'atients. If the analysis is 'erformed at the level of the individual while accounting for clustering in the data- theresults can be inter'reted for individual 'atients. See ection +8././ o( the CochraneHandoo0" Jethod o( analyi (or cl#ter5rando$i%ed trial.

#. $ample o" sensitivity analysis to investigate the

e*ect o" clusteringRead sections *4..- *4..1- and *4..4 of the Cochrane Handbook:

''ro&imate analyses of cluster5randomi3ed trials for a meta5analysis:

e6ective sam'le si3es# %&am'le of incor'orating a cluster5randomi3ed trial# and

''ro&imate analyses of cluster5randomi3ed trials for a meta5analysis: in;ating

standard errors.

A re&ie' a#thor can ad4#t a trial3 analyi (or cl#tering 'hen the trial3 analye did

not $a0e an ad4#t$ent (or the e2ect o( cl#tering, !ro&iding the (ollo'ing

in(or$ation i a&ailale"

I. the a&erage cl#ter i%eII. the intra5cl#ter correlation coecient (or the o#tco$e

III. the re#lt not ad4#ted (or cl#tering, (or e1a$!le a ri0 ratio and condence

inter&al, or n#$er o( !atient 'ith the e&ent and the n#$er o( !atient in

each treat$ent gro#!.

O(ten the intra5cl#ter correlation coecient i not re!orted in any trial article o( a

re&ie' and cannot e calc#lated y hand to gi&e an a!!ro1i$ate intra5cl#ter

correlation coecient. In thee cae a eniti&ity analyi can e !er(or$ed #ing a

range o( !la#ile &al#e (or the intra5cl#ter correlation coecient to in&etigate

'hether the re#lt o( a ingle trial 'o#ld change i( cl#tering had een ta0en intoacco#nt.

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The Cochrane handoo0 decrie $ethod and !ro&ide an e1a$!le o( ho' to ad4#t

the re#lt (or cl#tering #ing an e2ecti&e a$!le i%e a!!roach or an e7#i&alent

a!!roach that inKate the tandard error. An e1a$!le o( ho' to !er(or$ the

eniti&ity analyi #ing a range o( !la#ile &al#e i de$ontrated elo' aed on

the re&ie' ?Laccine (or !re&enting anthra13.

The ri0 ratio and the tandard error o( the nat#ral logarith$ o( the ri0 ratio can ecalc#lated #ing the (ollo'ing (or$#lae aed on the re#lt o( a ingle trial.

%reatment 'ontrol

vent a

on3event

c d

For the anthra1 re&ie', the t#dy ?@#rgao& +M83 $ea#red the o#tco$e ?cae o(

anthra13 a a dichoto$o# o#tco$e and !reented the re#lt ta#lated elo'.

!cari4cationvaccine

o vaccine

Anthra$case

: +=

on3

anthra$::+M :M

The ri0 ratio and the tandard error o( the nat#ral logarith$ o( the ri0 ratio can ecalc#lated to e ;.-:8 and ;.:;:: re!ecti&ely a (ollo'"

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For thi re&ie', the a&erage cl#ter i%e i eti$ated to e 8-. Thi &al#e 'aotained y di&iding the n#$er o( !atient in the t#dy y the n#$er o( cl#ter inthe t#dy. An eti$ate o( the intra5cl#ter correlation coecient 'a not !ro&ided ythe trial article or the trial in&etigator.

A range o( &al#e (or the intra5cl#ter correlation coecient 'ere entered into a e1cel

!readheet a ho'n elo'. The &al#e o( the ICC #ed in a !li$inary in&etigateranged (ro$ ; to ;.-. The Cochrane handoo0 reco$$end that &al#e lo'er than;.;+ are ty!ical.

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The

deign e2ect 'a calc#lated on the ne1t ro' (or each col#$n in t#rn #ing the

(or$#la"

'here $ i the a&erage cl#ter i%e and ICC i the intra5cl#ter correlation coecient.

On the ne1t ro', the tandard error (or the nat#ral logarith$ o( the ri0 ratio

calc#lated ao&e );.:;::* 'a $#lti!lied y the 7#are root o( the deign e2ect (or

each col#$n in t#rn, that i,

O#tide o( the tale o#ndarie in e1cel, the log ri0 ratio 'a calc#lated y ta0ing the

nat#ral logarith$ o( the ri0 ratio, (or e1a$!le,

On the (ollo'ing ro' o( the tale, the lo'er condence inter&al (or the ri0 ratio 'a

calc#lated (or each col#$n #ing the (or$#la"

And the #!!er condence inter&al (or the ri0 ratio 'a calc#lated #ing the (or$#la"

.

The nal re#lt can e !reented in a (oret !lot in Re&ie' Janager y entering the

log ri0 ratio and the inKated tandard error #ing the generic in&ere &ariance

o#tco$e $ethod.

St#dy na$e #ch a ?ICC;.;+3 $#t e entered a re(erence. The (oret !lot can

then e a&ed on a co$!#ter a a !ict#re and then reinerted into the Re&ie'

Janager le a a g#re. Thi allo' the (oret !lot to e deleted (ro$ data and

analye and the #n'anted re(erence )e.g. ICC;.;+* to e deleted (ro$ the re&ie'.

Page 1( o( 15

ntra3cluster correlationcoe6cient

0 0.001 0.002 0.005 0.01 0.02

Design e*ect+.;;;; +.8+; -./=-+ .::+ M.+;/

+.=-;

:

n7ated standard error;.:;:: ;.8:M/ ;.M=;- +.;88 +.-+M +.8;

8oer con4dence interval"or ris) ratio

;.;: ;.;M;- ;.;::- ;.;/+: ;.;+:M ;.;;:8

+pper con4dence interval"or ris) ratio

;.8=:M ;.-/ +.+M= -.;8+; .+/;

++.:/

M


15/15


Thi (oret !lot de$ontrate that i( cl#tering i not ta0en into acco#nt )i.e. 'hen

ICC;* the ri0 o( anthra1 i ignicantly lo'er in the &accinee a co$!ared to the no

&accinated gro#!. Ho'e&er, 'hen e&en a $all a$o#nt o( cl#tering i ta0en into

acco#nt )i.e. ICC;.;;-* the re#lt i no longer tatitically ignicant.

9repared by: Sarah Donegan, Statitical Editor

Date: 9an#ary -;+;

Page 15 o( 15

Documents

Cluster Randomised Trials Guide_Feb2010_0