Investigation Regarding the Correlation Between HDI and ... · HL Biology IA Anthony Hans Jan 2016...

HLBiologyIA AnthonyHans Jan2016

InvestigationRegardingtheCorrelationBetweenHDIandMortalityRatesduetoStroke

ResearchQuestion

WhatisthecorrelationbetweenHDIandmortalityrateduetostroke(measuredinnumberofdeathsper

100,000ofpopulation),incountrieswithaHDIofabove0.75?

BackgroundResearch

Stroke is a cardiovascular disease that involves a lack of blood flow to the brain (National Stroke

Association,n.d.).Thiscanoccurinseveralways:hemorrhagicstrokesoccurwhenaweakbloodvessel

inthebrainleaks,or ifananeurysm(a localizedswellingofabloodvessel)bursts insidethebrain;an

embolicstrokeoccursifaplaqueorclotfragmentformedelsewhereinthebody,travelsupthebrainand

blocksasmallbloodvesselthere;andathromboticstrokeiscausedbyaclotthatformedinsideoneof

thebrain’sbloodvessel.Alldeprivesectionsofthebrainfromreceivingsufficientoxygen,resultinginthe

deathofthebrain’sneurons.Collectively,allofthedifferenttypesofstrokeskillsixmillionindividuals

peryearworldwide(WorldHeartFoundation,2016).

Stroke, and other diseases such as coronary heart disease and Alzheimer’s disease, are non-

communicable;thatis,theyarenottransmittedfrompersontoperson,asinfectiousdiseasescarriedby

virusesorbacteriaare(WorldHealthOrganization,2015). Instead,theyarecausedduetoriskfactors,

suchphysicalinactivityorsmoking.Forthisreason,advancestechnologyandcivilengineeringwhichhas

helped inpreventingand curing transmissiblediseases (examplesbeingvaccines limiting theeffectof

bacterial/viraldiseases, andproper sewage treatment improvingpublichygieneand thereforehealth)

Figure1:Diagramshowingahemorrhagicstrokeinvolvingananeurysm

ALL TEXTS BELONG TO OWNERS.TAKEN FROM WWW.INTERNALASSESSMENTS.WORDPRESS.COM

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maynotnecessarilyworktoslowthegrowingprevalenceofnon-communicablediseases,whicharenot

causedbytransmissions.

Inthisinvestigation,HDI(humandevelopmentindex)willbeusedasthemetricbywhichdevelopmentis

measured. This is an index incorporating education, GNI per capita, and healthcare, using various

indicators to measure each component and therefore the overall HDI (Human Development Report,

2015).AnHDIvalueof0.75orhighercanthereforebeareasonableindicatorofadevelopedcountry.

Although certainly not as prominent as other non-communicable diseases, such as coronary heart

diseaseorcancer–bothofwhicharetheleadingcausesofdeathinmostdevelopedcountries–strokeis

bynomeansinsignificant.Evenifastrokeattackdoesnotclaimthelivesofitsvictims,thedevastationit

sooftencauses to theafflictedand their familiesarehugelyparalyzing.Therefore, Ihavedevoted this

investigationtothestudyofstroke’sprevalence,inhopesofbetterunderstandingitinthelargerpicture.

Therefore, this research aims to determine the impact of human development on the number of

mortalities caused by strokes; where human development is measured by HDI, and the number of

mortalitiesistakenperannumandper100,000.

Hypothesis

ItcanbepredictedthereisanegativecorrelationbetweentheHDIofacountryandthenumberoflethal

strokecasesthere.

This is because when very high HDI countries are concerned, strokes aremore easily treatable with

advanced healthcare, allowing stroke patients a higher recovery rate. Therefore, despite a higher life

expectancyandmorepeople suffering fromstrokes,highlydevelopedcountriesmightbeable to treat

strokesmore easily thanotherdiseases such as cancer or coronaryheart disease, hence reducing the

mortalityrateduetostrokes

Therefore,thehypothesesforstatisticaltestingareasfollows:

NullHypothesis:HDIhasnoimpactonthemortalityrateduetostroke.

AlternativeHypothesis:HDIwillhaveanegativecorrelationonthemortalityrateduetostroke


3

Materials

l MicrosoftExcel(usedforallcalculationsanddataprocessing)

l HDIdatabase(for this, theHumanDevelopmentReportspublishedby theUNwillbeused,which

maybefoundinthislink:http://hdr.undp.org/en/data)

l WHO database on mortalities due to cerebrovascular diseases (may be found in this link:

http://www.who.int/healthinfo/global_burden_disease/estimates/en/index1.html, note that the

deathestimatesfor2000and2012isused)

l World Bank database on total population (may be found in this link:

http://databank.worldbank.org/data/home.aspx)

Data from these sources are chosen for two reasons: reliability (as the UN and World Bank can be

consideredasreliableandtrustworthysourcesforsuchdataduetothenatureoftheirorganization),and

alackofotherdatabases.

Methodology&TrialInvestigation

The following trial investigationwasconductedwithaselectionofsevennations,whichcanalsobe

used to demonstrate the methodology of this investigation. These countries are: Austria, Denmark,

Germany, Greece, Hungary, Portugal, and Spain. These countries are chosen as they are all European

OECDnations,andthereforeshouldhavereasonablysimilarculturalandeconomicstatus,reducingthe

possible impact of unrelated outside factors such as lifestyle habits or dietary preferences. The

correlationshouldthereforebereasonablystrong,demonstratingthatthisinvestigationwillwork.

Firstly,dataregardingthepopulation,humandevelopmentindex,andpopulationwillbeobtainedfrom

their respectivedatabases for theyears2000and2012 (theonlyyearswhen theWHOhaspresented

dataregardingcausesofmortalityontheirwebsite):

Table1:Rawdatashowingtheestimateddeathcountsduetostroke,populationandtheHDIofselectedcountriesinthespecifiedyears

CountryHumanDevelopmentIndex Estimateddeathcountsdueto

stroke(in'000sofdeaths) Population

2000 2012 2000 2012 2000 2012 Austria 0.836 0.884 8.8 5 8,011,566 8,429,991Denmark 0.862 0.921 5.2 3.6 5,339,616 5,591,572Germany 0.855 0.915 82.4 59.9 82,211,508 80,425,823Greece 0.799 0.865 22.9 20.7 10,805,808 11,045,011Hungary 0.769 0.823 18.8 13.3 10,210,971 9,920,362Portugal 0.782 0.827 22.8 12.8 10,289,898 10,514,844Spain 0.827 0.874 36.6 29.6 40,263,216 46,773,055


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Tocalculatedeathrates,theestimateddeathcountsduetostrokecanbedividedbythepopulation.This

is the death rate due to stroke per person; to find the more conventional death rate per 100,000

population,thenumbercanbemultipliedby100,000.

Samplecalculations:Austria’sdeathrateduetostrokeper100,000populationin2000

𝐷𝑒𝑎𝑡ℎ 𝑟𝑎𝑡𝑒 𝑝𝑒𝑟 𝑝𝑒𝑟𝑠𝑜𝑛 =𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 𝑑𝑒𝑎𝑡ℎ 𝑐𝑜𝑢𝑛𝑡

𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛

=8.8

8011566= 0.001098412 𝐷𝑒𝑎𝑡ℎ 𝑟𝑎𝑡𝑒 𝑝𝑒𝑟 100,000 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 𝐷𝑒𝑎𝑡ℎ 𝑟𝑎𝑡𝑒 𝑝𝑒𝑟 𝑝𝑒𝑟𝑠𝑜𝑛 × 100,000 = 0.001098412 × 100,000 = 109.8 (Note that the final result is in1decimalplace,as thedata foundondeathcounts isalso in1decimal

place.)

Table2:Processeddatashowingthemortalityratescausedduetostrokes

CountryMortalityratesduetostrokeperperson

Mortalityratesduetostrokeper100,000

population2000 2012 2000 2012

Austria 0.001098412 0.000593120 109.8 59.3Denmark 0.000973853 0.000643826 97.4 64.4Germany 0.001002293 0.000744786 100.2 74.5Greece 0.002119231 0.001874149 211.9 187.4Hungary 0.001841157 0.001340677 184.1 134.1Portugal 0.002215765 0.001217327 221.6 121.7Spain 0.000909018 0.000632843 90.9 63.3

Fromhere,itisasimplematterofaveragingthedeathratesandHDIforbothyears,thencomparingthe

twovaluesforcorrelation:


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Table3:Averagemortalityratesper100,000populationduetostrokeandHDIofselectedcountriesofduringtheyears2000and2012

CountryAveragehumandevelopment

index

Averagemortalityrateduetostroke

per100,000population

Austria 0.860 84.6Denmark 0.891 80.9Germany 0.885 87.4Greece 0.832 199.7Hungary 0.796 159.1Portugal 0.804 171.7Spain 0.851 77.1

Theinvestigationwillfollowexactlythesamemethod,exceptwithalargernumberofcountries.

InvestigationandResults

Thedatabaseused inobtainingHDI informationdivides countriesbasedon four categories: veryhigh

HDI countries (countrieswith a HDI above 0.8 as of 2014), high HDI countries (between 0.7 to 0.8),

medium HDI countries (between 0.55 to 0.7) and low HDI countries (below 0.55). Therefore, the

0.0

50.0

100.0

150.0

200.0

250.0

0.780 0.800 0.820 0.840 0.860 0.880 0.900Deathrateduetostrokeper100,000population

Humandevelopmentindex

Chart1:therelationshipbetweenHDIandmortalityratesduetostrokeper100,000

populationintrialnations


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countriescategorizedashavinga“veryhighHDI”willbeusedinthisinvestigation,asrelativelyfewof

them have a HDI below 0.75 during 2000 (which is theminimumHDI used for this investigation, as

statedintheresearchquestion).Astherearerelativelyfewcountriesinthiscategory–only49–anda

fewofthemeitherlackdata(suchasLiechtenstein)orhaveapopulationthatisrelativelysmall(suchas

SingaporeorHongKong),randomsamplingisnotnecessary;only18ofthesecountrieshavesufficient

data,anHDIthatisconsistentlyabove0.75andapopulationsizegreaterthan10millionsince2000,so

these18countriesshallbeused.

Theresultsareasfollows:

Table4:RawdatashowingtheHDI,deathcountsduetostrokeandtotalpopulationofnations

withHDIsabove0.75ontheyears2000and2012

CountryHumandevelopment

index

Deathcountduetostroke(in'000sof

deaths)Totalpopulation

2000 2012 2000 2012 2000 2012 Argentina 0.762 0.831 27.4 28.2 19,153,000 22,728,254Australia 0.898 0.932 12.2 11.0 37,057,453 42,095,224Belgium 0.874 0.889 8.6 7.4 10,251,250 11,128,246Canada 0.867 0.910 15.5 13.5 30,769,700 34,751,476Chile 0.752 0.827 7.4 8.4 15,170,387 17,388,437

CzechRepublic 0.821 0.867 16.9 10.4 10,255,063 10,510,785France 0.848 0.886 40.9 34.4 60,912,498 65,659,790

Germany 0.855 0.915 82.4 59.9 82,211,508 80,425,823Greece 0.799 0.865 22.9 20.7 10,805,808 11,045,011Italy 0.829 0.872 67.3 58.7 56,942,108 59,539,717Japan 0.857 0.888 132.1 120.6 126,843,000 127,561,489Korea

(Republicof)0.821 0.893 41.6 27.8 22,840,218 24,763,353

Netherlands 0.877 0.920 12.5 8.8 15,925,513 16,754,962Poland 0.786 0.838 66.8 64.5 38,258,629 38,063,164Portugal 0.782 0.827 22.8 12.8 10,289,898 10,514,844Spain 0.827 0.874 36.6 29.6 40,263,216 46,773,055UnitedKingdom

0.865 0.901 62.1 46.3 58,892,514 63,700,300

UnitedStates 0.883 0.912 169.3 133.6 282,162,411 314,102,623


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Table5:Processeddatashowingthemortalityratecausedbystrokeintheselectednationsin2000and2012

CountryMortalityrateduetostrokeperperson Mortalityrateduetostrokeper

100,000population2000 2012 2000 2012

Argentina 0.001432383 0.001241697 143.2 124.2Australia 0.00032908 0.00026096 32.9 26.1Belgium 0.000840013 0.000661172 84.0 66.1Canada 0.000503748 0.000387472 50.4 38.7Chile 0.000490413 0.000482589 49.0 48.3

CzechRepublic 0.001647081 0.000988891 164.7 98.9France 0.00067176 0.000524081 67.2 52.4

Germany 0.001002107 0.000744576 100.2 74.5Greece 0.002114838 0.001870679 211.5 187.1Italy 0.001182507 0.000985131 118.3 98.5Japan 0.001041133 0.000945319 104.1 94.5

Korea(Republicof) 0.001819974 0.00112458 182.0 112.5Netherlands 0.000787218 0.000522311 78.7 52.2

Poland 0.001745275 0.001693969 174.5 169.4Portugal 0.00221199 0.001213221 221.2 121.3Spain 0.000909327 0.000632348 90.9 63.2

UnitedKingdom 0.001054875 0.000726532 105.5 72.7UnitedStates 0.000600084 0.000425269 60.0 42.5

Table6:theaverageHDIandmortalityratesduetostrokeduringthe

years2000and2012

Country Averagehumandevelopmentindex

Mortalityrateduetostrokeper100,000

populationArgentina 0.796 133.7Australia 0.915 29.5Belgium 0.881 75.1Canada 0.889 44.6Chile 0.790 48.7

CzechRepublic 0.844 131.8France 0.867 59.8

Germany 0.885 87.3Greece 0.832 199.3Italy 0.850 108.4Japan 0.872 99.3

Korea(Republicof) 0.857 147.2Netherlands 0.899 65.5

Poland 0.812 172.0Portugal 0.804 171.3Spain 0.850 77.1

UnitedKingdom 0.883 89.1UnitedStates 0.897 51.3ALL TEXTS BELONG TO OWNERS.

TAKEN FROM WWW.INTERNALASSESSMENTS.WORDPRESS.COM

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Herewecanobservethatthereisoneoutlierwithamortalityrateof48.7per100,000duetostroke,and

aHDIof0.790(thevaluefoundinthebottomleftoftheotherdatapointsonthegraph);thisbelongsto

Chile. If this is taken out of consideration, we can see that the scatter graph forms a loose linear

correlation, as displayed on the graph. The linear correlation therefore allows the use of a Pearson’s

product-momentcoefficientforstatisticaltesting.

StatisticalTesting

To conduct a Pearson’s correlation test, some values must be assigned: the variable X can be the

mortalityrateduetostroke,whereasYisthehumandevelopmentindex,andNdenotesthenumberof

countries.Thetotalsumofeachcolumnisthenfound.Then,newcolumnsforthevaluesofXY,X2,andY2

isneeded.Theresultisasfollows:

y=-803.25x+787.78R²=0.37128

0.0

50.0

100.0

150.0

200.0

250.0

0.750 0.770 0.790 0.810 0.830 0.850 0.870 0.890 0.910

Mortalityrateper100,000populationcausedbystroke

Humandevelopmentindex

Chart2:ScattergraphshowingtherelationshipbetweenHDIandMortalityrateduetostrokein

countrieswithHDIsabove0.75


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Table7:Pearson’sproductmomentcorrelationtestontheresultsontable5

N X Y XY X2 Y2

1 133.7 0.796 106.425 17875.7 0.634

2 29.5 0.915 26.993 870.3 0.837

3 75.1 0.881 66.163 5640.0 0.776

4 44.6 0.889 39.649 1989.2 0.790

5 48.7 0.790 38.473 2371.7 0.623

6 131.8 0.844 111.239 17371.2 0.712

7 59.8 0.867 51.847 3576.0 0.752

8 87.3 0.885 77.261 7621.3 0.783

9 199.3 0.832 165.818 39720.5 0.692

10 108.4 0.850 92.140 11750.6 0.723

11 99.3 0.872 86.590 9860.5 0.761

12 147.2 0.857 126.15 21667.8 0.734

13 65.5 0.899 58.885 4290.3 0.808

14 172.0 0.812 139.664 29584.0 0.659

15 171.3 0.804 137.725 29343.7 0.647

16 77.2 0.850 65.620 5959.8 0.723

17 89.1 0.883 78.675 7938.8 0.780

18 51.3 0.897 46.016 2631.7 0.805

Sum 1791.1 15.423 1515.333 219997.4 13.241

Fromhere,thefollowingequationisusedtofindthePearson’scorrelationvalue:

𝑟 =𝑛 𝑥𝑦 − ( 𝑥)( 𝑦)

(𝑛 𝑥! − ( 𝑥)!)(𝑛 𝑦! − ( 𝑦)!)

Utilizingthisformula,thefollowingresultmaybefound:

𝑟 =18 1515.333 − (1791.1)(15.423)

18 219997.4 − 1791.1! 18 13.241 − 15.423!

𝑟 = −0.586

Thisvaluemeansthatthereisareasonablystrongnegativecorrelationbetweenthehumandevelopment

indexofadevelopedcountry,andthemortalityratescausedbystroke.Furthermore,itisfoundthatina

Pearson’scorrelationtest,thecriticalvalueforacorrelationwith17degreesoffreedom(foundbythe

numberoftrials,18,minus1),andalevelofconfidenceof0.05,is0.482(StatisticsSolutions,n.d.).Ther

valueobtainedfromthisinvestigationhasahigherabsolutevaluethanthis;therefore,wecanrejectthe


10

nullhypothesisandconcludewiththealternativehypothesis,whichstatesthatHDIwillhaveanegative

correlationonthemortalityrateduetostroke.

Conclusion

Torestate the researchquestion:What is the correlation betweenHDI andmortality rate due to

stroke (measured in number of deaths per 100,000 of population), in countrieswith a HDI of

above0.75?

This investigation has found that HDI has a negative correlationwithmortality rate due to stroke in

developedcountries, ina linear trend,supporting thehypothesismadeearlier.Abiologicalexplanation

forthismightbethatstrokesareeasiertotreatthanothernon-communicablediseases,suchascancer.

This means that, even though a greater proportion of people in developed countries will have been

exposed to more risk factors for strokes (such as trans fats, sedentary behavior, etc.), and advanced

healthcare system can still compensate by improving the chance of recovery, whereas another non-

communicable disease such as cancer is much more difficult to treat, and hence is more difficult to

compensatewithgoodhealthcarestandards.Thissaysnothingoftheeconomicandsocialrepercussions

ofcontractingstrokes,evenwhenonerecovers,whichisbestreservedforanotherinvestigation.

ThisissupportedbyastudypublishedonBioMedCentral(Wu,WooandZhang,2013);inthisstudy,a

correlationbetween socioeconomic statusand stroke isbeing tested, rather thanHDI.However, these

two variables are reasonably similar as ameasure of a population’swell-being, and can therefore be

assumed to be somewhat comparable. This study has claimed that, whereas an improvement in

socioeconomicstatus increasedstrokemortality in lessdevelopedareas, theopposite is true formore

developedcountriesandregions,hencesupportingthisinvestigation’sfindings.

Evaluation

Astrengthofthisinvestigationisthestrongreliabilityofthedataused;sincethecountriesusedforthis

investigationarerelativelymodernizedandhavepopulationslargerthan10million,itcanbeexpected

thatthedatacollectedisnotonlyaccurate,butrepresentative.Thereisalsoasufficientrangeanddata

collectedtodrawaconclusionfrom.

However,thisinvestigationdoeshavesomeissues:


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Table8:LimitationsofthisinvestigationLimitation Significance Possibleimprovement

Onlytheyears2000and2012wereused,asthesearetheonlyyearsthatthedatabaseshadincommon.

Thislimitsthereliabilityofeachofthecountry’sdatapoints,asonlytwosamplesaretakenpercountrytoformanaverageofthecountry’smortalityrateandHDI,whichmaybenon-representative.

Datafromotheryearsmaybecollecteddirectlyfromthevariouscountry’snationalhealthwebsites,whichmayyielddatafromyearsotherthan2000and2012forallnations.

Samplesizeisrathersmallat18countries.

Thismayhaveaneffectonthestatisticaltesting,whichthereforeweakenstheconclusionmadedrawnfromtheresults.

Countrieswithsmallerpopulationsizescanbeconsidered–suchasabove8million,ratherthan10million.

Thecountriesusedfortheinvestigationhadveryfewcontrolledvariables.

Thecountriesinthisinvestigationvaryquitedramatically,fromthelargelyurbanUKtothemoresparselypopulatedCanada.Thishasledtoagreatamountofuncertaintyinthedata(evidentwithanR2valueoflessthan0.4).

Otherfactors,suchaspopulationdensity,climateandGDPpercapitamayalsobeconsideredandkeptsimilarfortheselectedcountries,thoughthismaylimitthesamplesize.

Whenconductingthisinvestigationagain,thefollowingchangesmayimprovetheresults:

§ Thelargernationsmaybeseparatedintotheirconstituentdistricts/states(forexample,theUScan

be separated into its 50 states, and whereas China’s national HDI may be relatively low, more

prosperousprovinces/districts such as Shanghai orTianjin canbe investigated), and thedata for

each regionmay be collected individually. Thismay dramatically increase the sample size of the

investigation–providedtheconstituentshaveasufficientlylargepopulationsize.

§ Theoverallsocialimpactofstrokecanbeinvestigatedalongsidethemortalityrate,usingindicators

suchastheaveragehospitalizationtimeforstrokecases,ormonetarycostsofoperations;thiswill

allowtheinvestigationtobettergaugetheprevalenceandsignificanceofstrokes.

§ Lessprosperouscountriescanbeinvestigatedaswell;thiswillleadtoaninvestigationofstrokeon

amuchbroaderscope,whichmayreveal the trendbetweenHDIandstroke-causedmortalities in

lessdevelopednations.


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Bibliography

WorldHealthOrganization,(2015).NoncommunicableDiseases–FactSheet.[online]Availableat:

http://www.who.int/mediacentre/factsheets/fs355/en/

WorldHeartFederation,(2016).Stroke.[online]Availableat:

http://www.world-heart-federation.org/cardiovascular-health/stroke/

NationalStrokeAssociation,(2017).HemorrhagicStroke.[online]Availableat:

http://www.stroke.org/understand-stroke/what-stroke

NationalHealthService,(2015).Whatarecerebrovasculardiseases?[online]Availableat:

http://www.nhs.uk/conditions/cerebrovascular-disease/Pages/Definition.aspx

HumanDevelopmentReports,(2015).HumanDevelopmentData(1980–2015).[online]Availableat:

http://hdr.undp.org/en/data

WorldHealthOrganization,(2017).Estimatesfor2000–2012.[online]Availableat:

http://www.who.int/healthinfo/global_burden_disease/estimates/en/index1.html

TheWorldBank,(2017).Explore.Create.Share:DevelopmentData.[online]Availableat:

http://databank.worldbank.org/data/home.aspx

StatisticsSolutions,(n.d).TableofCriticalValues:PearsonCorrelation.[online]Availableat:

http://statisticssolutions.com/table-of-critical-values-pearson-correlation/

Wu, S., Woo, S., and Zhang, X., (2013). Worldwide socioeconomic status and stroke mortality: an

ecologicalstudy.BioMedCentral.[online].Availableat:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3695775/

HumanDevelopmentReports,(2015).HumanDevelopmentIndex(HDI).[online]Availableat:

http://hdr.undp.org/en/content/human-development-index-hdi


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