corin badiu, 2007 metodologia cercetării ştiinţifice metodologia cercetării ştiinţifice...
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Corin Badiu, 2007
Metodologia cercetMetodologia cercetăării rii şştiintiinţţificeifice
Ipoteza de lucruOrganizarea studiului
Tipuri de studii
Obiective
• Dobandirea abilitatilor de cercetare• Redactarea unui protocol de 10 pagini pentru
un studiu real• Analiza altor studii (peer review)
Tipuri de Studii
• Nu sunt cea mai buna alegere pentru acest curs Studii fundamentale: molecule, celule, soareci Cost-eficienta, meta-analize Cercetare calitativa
• Ideal Un studiu observational (sau experiment) ce
implica pacienti
Sectiuni ale protocolului de studiu
• Ipoteza de lucru• Semnificatia (fondul)• Designul studiului• Populatia de studiu si recoltarea datelor;
controlul de calitate al datelor• Variabile si masuratori• Analiza statistica a datelor• Etica cercetarii medicale
Ipoteza de lucru
• Toate studiile incep cu o problema, intrebare fara raspuns
• Scopul este alegerea unei intrebari de cercetare relevante, ce poate fi transformata in proiect
Problema studiului
• Format pentru un studiu descriptiv “Intr-o populatie de [populatie de studiu ],
care este prevalenta (sau media, mediana, etc.) [variabila dependenta]?”
• Majoritatea studiilor au mai mult decat o problema de evaluat si rezolvat
• Protocolul de cercetare deriva din problema studiului
• Format uzual (studii analitice):
“Intr-o populatie de [populatie de studiu], exista o asociere intre [variabila dependenta] cu [variabila independenta]?”
Problema studiului
Identificati problema studiului enuntata in rezumat
Acute respiratory tract infections caused by Streptococcus pneumoniae are a leading cause of morbidity and mortality in young children. We evaluated the efficacy of a 9-valent pneumococcal conjugate vaccine in a randomized, double-blind study in Soweto, South Africa. At 6, 10 and 14 weeks of age, 19,922 children received the 9-valent pneumococcal polysaccharide vaccine conjugated to a noncatalytic cross-reacting mutant of diphtheria toxin (CRM197), and 19,914 received placebo…
Klugman KP, Madhi SA, Huebner RE, et al. A trial of 9-valent pneumococcal conjugate vaccine in children with and without HIV infection.
N Engl J Med 2003; 349:1341-8.
In a population of South African infants is immunization with a 9-valent pneumococcal conjugate vaccine associated with invasive pneumococcal disease?
Intr-o populatie de [populatie de studiu], exista o asociere intre [variabila dependenta] si [variabila independenta]?”
Originile unei probleme de cercetare
• Cercetarea literaturii Discutia problemelor din literatura
• A fi deschis la idei si tehnici noi Importanta invatarii
• Imaginatia
Caracteristicile unui studiuFINER
• Fezabil
• Interesant pentru investigator
• Nou
• Etic
• Relevant
Caracteristicile FINERCriterii de Fezabilitate
• Numar adecvat de subiecti
• Expertiza technica adecvata
• Realizabil ca resurse de timp si bani
• Resurse umane calificate adecvat
Caracteristicile FINERCriterii de Interes
• Studii cu impact populational
• Detalierea a noi mecanisme de boala
• Studii de eficienta terapeutica pentru metode noi
Caracteristicile FINERCriterii de Noutate
• Confirma sau anuleaza cercetari anterioare
• Extinde cercetari anterioare
• Furnizeaza noi date
• Consimtamant informat !!!• Protejeaza pacientii sau NU ii expune unui risc
suplimentar• Excluderea imediata / oprirea studiului in cazul
unor efecte adverse severe
Caracteristicile FINERCriterii de Etica
• Pentru cunoasterea stiintifica
• Pentru clinicieni, sanatatea publica sau politicile de sanatate
• Pentru directii de cercetare viitoare
Caracteristicile FINERCriterii de Relevanta
Probleme si solutii:Planul nu este FINER
• Nefezabil Prea larg Prea putini pacienti disponibili Metode sofisticate, peste abilitatile
dovedite de investigator Prea scump
• Fara interes, noutate sau relevanta• Evaluare etica inadecvata
Probleme si solutii:Planul nu este Fezabil
• Prea larg Un set mai mic de variabile Se delimiteaza mai mult domeniul
• Insuficienti subiecti disponibili Extinde criteriile de includere Schimba criteriile de excludere Adauga alte surse de subiecti Extinde durata de inrolare Foloseste strategii de scadere a lotului
• Metode in afara abilitatilor investigatorului Colaborare cu colegi cu aptitudini Consultarea de experti si reluarea literaturii pentru
metode alternative Invata si practica aptutidinile cerute de studiu
• Prea scump Scade costurile designului de studiu
• Mai putini subiecti si masuratori• Detaliu mai mic al masuratorii• Mai putine vizite de urmarire
Probleme si solutii:Planul nu este fezabil
• Neinteresant, vechi sau irelevant Consulta mentorul Modifica problema cercetata
• Abordare etica nesigura Consulta comitetul de etica Modify the research question
Probleme si solutii:Planul nu este FINER
Probleme si solutii
• Planul de studiu este vag Rescrie planul de cercetare mai amanuntit
Detaliaza din planul de studiu• Cum vor fi selectati subiectii si lotul martor• Cum vor fi masurate variabilele
Probleme si solutii: exemple
• Ce relatie exista intre depresie si sanatate?
• Consumul de carne rosie determina cancer?
• Scaderea colesterolului seric previne boala cadiaca ischemica?
Anatomia Cercetarii Clinice
Fiziologia cercetarii clinice: Cum are loc?
Se folosesc masuratorile intr-o proba / esantion /lot de studiu
pentru a extrage inferente despre
fenomene (variabile) intr-o populatie
Predictor* Rezultat
Variabile de confuzie*
Modificatori ai efectului*
Tipuri de variabile
*Considerate general ca expunere la factori de risc
Problema de studiu
• In studii descriptive:
“Intr-o populatie de [study population], care este prevalenta [outcome variable]?”
• In studii analitice :
“Intr-o populatie de [study population], este [predictor variable] asociata cu [outcome variable]?”
Tipuri de studii clinice
• Studii fara variabile Studii de caz, serii de cazuri, editoriale,
opinii / comentarii, rapoarte review
• Studii cu o singura variabila Studii descriptive
• Studii cu ≥2 variabile Experimente Studii observationale Meta-analize si review-uri sistematice
Ierarhia tipurilor de studii clinice
Descriptive studies
Experimental studies
Cohort Case-control Cross-sectional
Observational studies
Analytic studies
Conceptie (study design) legata de obiectivele studiului.
Conceptie inainte de colectarea si analiza datelor
Concepta studiului este importanta intrucat permite o crestere a validitatii si reducerea erorilor.
Variabila predictor(independenta)
Variabila rezultat (dependenta)
Variabile
Factori care influenteaza conceptia studiuluiFactori care influenteaza conceptia studiului
1. Obiectivele studiului – intrebarile cercetarii
2. Epidemiologia bolii / expunerii - rara / comuna
3. Aspecte etice
4. Resurse- bani, oameni, infrastructura
Ce tip de studiu este mai adecvat?
• Telefonia mobila determina cancer cerebral?
• Dieta afecteaza riscul de cancer mamar?
• Fumatul pasiv determina cancer pulmonar?
Tipuri de study design
1. Experimental/ Quasi-experimental sau observational
2. Directia studiului in relatie cu expunerea si aparitia bolii
3. Cantitativ /Calitativ
Women's Health Initiative (1991)
Ar trebui sa primeasca substitutie cu estrogeni femeile postmenopauza?
http://www.nhlbi.nih.gov/whi/
Subiecti: femei postmenopauza
Predictor: “estrogeni”
Rezultat: ?
Ar trebui sa primeasca substitutie cu estrogeni femeile postmenopauza?
Women's Health Initiative (1991)
Ameliorarea problemei de cercetare
Tratamentul cu estrogeni previneaccidentul coronarian la femei postmenopauza?
Subiecti: femei postmenopauzaPredictor: tratament cu estrogeni vs no treatRezultat: accident coronarian
FINER?
Fezabil
Interesant
Nou
Etic
Relevant
7 tipuri de studii
1. Randomized controlled trial 2. Cohort study 3. Case-control study4. Sample survey or cross sectional
study5. Ecologic or trend study 6. Case report or series 7. Qualitative research
Ncesitatea desing-ului
• Trial clinic randomizat Puncte finale Interes primar
• Studiu observational Cross-sectional Case control Cohorta
1. Studii Experimental / Interventionale -
Randomized controlled trial (RCT)
• Evaluate new forms of therapy and prevention New drugs and other treatment of disease New medical and health care technology New methods of primary prevention New programs for screening and early detection of
disease New ways of organizing and delivering health services
( community trial ) Impact of new policies in health care and health care
financing ( community trial )
Randomized controlled trial
• Cel mai bun design- randomizare, eroare de selectie minima
(dar nu zero);
• Nu este etic: daca interventie poate dauna, rezultat clinic slab
• Nu este practic – boli rare, efect rar;
• Participarea subiectilor la studiu este cruciala.
Randomized Controlled Trial
Elements Design
Randomization
New treatment Current treatment
/no treatment
Defined population
ImprovedNot
improved Improved Not improved
Intervention
Outcome
Selection of subjects -similar features -inclusion/exclusion criteria
Allocation of subjects
Data collection
Masking (blinding)
RCT
• Blinding Double- subjects & investigators Single – subjects (placebo effect) Triple blind- subjects & investigators & statisticians
• Outcome/endpoint improvement ( desired effect) and side effects must be explicitly defined measured comparably in all study groups
• Multi-centre trial
• Comply with GCP requirements
• Clinical trials/ community trials
• Results of RCT- benchmark- good clinical practice (GCP) , clinical governance, treatment protocol.
Types of RCT:• Superiority or equivalence trials A
• Parallel-most common B
• Cross over- Planned –washout
period
A B
B A- Unplanned
Surgical Medical randomized
randomized
Refuse surgery Require surgery
Analyze outcome by intention to RxNo surgerySurgery
Limite
1. ? effective in uncontrolled community
2. consent – refusal- automatic selection
(people who participate are different from those who do not)
3. Non compliance ( people who are compliant are very different from
those who are not)
- drop-outs: no adherence to experimental regimen, loss to f/u
- drops-in: no adherence to control regimen
4. Compliance -Need monitoring
5. Most costly
Studii observationaleStudii observationale
1. Cohort study
2. Case-control study
3. Cross sectional study
4. Ecologic or trend study
5. Case report or series
6. Qualitative research
Direction, timing , +/- control
Studiu de cohorta
Subiecti 5000 femei cu varsta 55+ ani
Factor predictor: estrogeni post-menopausal?
Outcome: Incidenta accidentelor coronariene dupa 5 ani
de terapie
Cand este bun un studiu de cohorta?Cand este bun un studiu de cohorta?
• When there is good evidence of an association of the disease with a certain exposure
• When exposure is rare and incidence of disease among exposed is frequent
• When the time between exposure and disease is short
• When the investigator has a long life expectancy!
Cohorta
• Cohort: “any designated group of individuals who are followed or traced over a period of time”
• Free of the outcome at the beginning of follow-up (population at risk)
• Usually defined or divided by exposure status
Populatia la risc
• All subjects within a cohort must be free of the outcome at the start of the follow-up period
• All subjects must be at risk for developing the disease (population at risk)
Studii de cohorta Prospective vs. Studii de cohorta Prospective vs. RetrospectiveRetrospective
• Prospective
Cohort Study Better control of the
quality and quantity of the data
• less potential for bias
More time consuming More expensive
• Retrosepective Cohort Study Poorer control of the
quality and quantity of the data
• greater potential for bias
Less time consuming Less expensive
Pierderea din urmarire(Loss to Follow-up)
• Problem, especially if lost subjects are at higher/ lower risk for developing the outcome compared to other subjects
even worse if this problems is different with comparison groups
• < 60% follow-up is generally regarded with skepticism
Analiza datelor – studii de cohorta
Start with exposure, then follow to see whether
Disease +
Exposed +
Exposed -
Disease - total Incidence rate of disease
a b
c d
a+b
c+d
a/a+b
c/c+d
• Absolute risk = incidence of disease cases in exposed group / total population
• Relative risk=
• Taria asociatiei (Odds ratio) = ad/bc
Analiza datelor – studii de cohorta
incidence of dis among E+incidence of dis among E-
Limite
• Some exposure can change over time e.g. aging, life style (diet, smoking pattern), exposure to pharmaceutical agents, air pollution
• Changes on method over time- disease identification• Prospective - follow-up, thus long period • Costly • Potential bias
selection bias ( who has been exposed and who has not ) information bias – historical data bias in outcome assessment non-response and loss to f/u analytical bias
Cross-sectional design
Subiecti 2000 femei varsta 55+ ani
Predictor: Tratament post-menopausal cu estrogeni?
Rezultat: Istoric de accident coronarian?
Sample survey or cross sectional study :
• It is a survey of the frequency of disease and other characteristics in a defined population at one particular time.
• Focus on describing a state or process at a fixed time.
• Suitable for describing prevalence and distribution of heath problem in a community. (prevalence or health survey).
Sample survey or cross sectional study : - cont
• In clinical research, used in : Describing disease presentation (spectral description
study) Diagnostic test accuracy study Quality of care assessment.
• Generally efficient but large scale community survey can be expensive.
• Sometimes survey data given causal interpretation (pseudo-longitudinal) but liable to error, caution.
Advantages of Cross Sectional Study Design
• One stop shopping
• Less expensive
• Potentially can detect effect of exposure that do not vary over time
Disadvantages of Cross Sectional Study Design
• May not detect associations that for diseases with short duration that have cyclic or seasonal trends (e.g. some infectious diseases)
• May require over-sampling of low prevalence exposure or disease groups
Design Case-control
Subiecti / femei la menopauza Cazuri: 100 femei cu accident coronarian Controale: 100 femei fara patologie cardiaca
Predictor: Au luat estrogeni post-menopauza?
Rezultate: Cazuri vs controale
Controls
• Case Control Studies compare exposure history of cases and controls
• Controls provide exposure distribution of exposure (exposed and unexposed cohorts) in source population that gave rise to the cases in the study
• Biggest Problem: Identifying an appropriate control group
Sources for Controls
• Population Controls
• Neighborhood Controls
• Random-Digit Dialing
• Hospital-Based Controls
Nested Case Control Studies
• Every Case Control Study can be thought as being conducted within a cohort study Cases represent the outcomes of the cohort Controls provide estimate of exposure distribution
of cohort
• Traditionally, Nested Case Control Study usually refers to study that are conducted within the experience of a well-defined cohort study
2x2 Table
Case ControlExposure + a bExposure - c dTotal M1 M0
OR = (a/c) / (b/d) (a/c) / (K1/K0)
IRR
Hospital-Based Controls
• Most appropriate for hospital-based cases with ill-defined catchment area as source population
• Often chosen from diagnostic groups not thought to be related to the exposure better to choose more than one diagnostic
group for controls minimizes impact of a poor choice
Hospital-Based Controls
• History of diagnosis for different condition related to exposure is not grounds for exclusion Some cases may have the same history
• Assumption: catchment area for control diagnosis is same
as catchment area for cases control reflect exposure distribution for source
population of cases
Comparison of Case Control and Cohort Studies
• Primary Difference: Cohort Study involved complete
enumeration of the source population Case Control Study involved a sample
(controls) of the source population • Case Control Studies are modified Cohort
Studies
• When there is good evidence of an association between a certain exposure and the disease
• When disease is rare and exposure is frequent among exposed
• Advantage: Cost- relatively inexpensive Sample size –relatively small
When is a case control study warranted?
Analysis of data-case control study
Begin with cases with disease and controls without
disease, then measure past exposure Disease +
Exposed +
Exposed -
Disease - total
a b
c d
a+b
c+d
Odd ratio= a/a+c / b/b+d= ad/bc
Proportion of exposed
a/a+c b/b+d
Limitation
• Selection of appropriate controls
• Recall bias
- Human ability to recall
- Recall bias (Case may remember their exposure more than controls do)
Etic?
• Echivalenta (nu este sigur daca domina beneficii sau riscuri)
Beneficii ale terapiei de substitutie• Scad simpotomele de climax• ? Preventia fracturilor• ? Preventia BCI• ? Preventia Alzheimer• ? Cresterea calitatii vietii
Riscuri• ? trombo-embolism pulmonar• ? Cancer mamar
Relevant?
• Estrogeni / estroprogestative• Decizia afecteaza o mare parte din
populatie
TRECUT PREZENT
Cazuri
Controale
Yes
Yes
No
No
Cancer mamar
Fara cancer de san
A primit HRT?
Case report or series :
• Description of one or several cases in which no attempt is made to answer specific hypotheses or to compare results with another group of cases. classical clinical study; its value probably
under rated (Pickering Lancet 19##)
Case report or series
• Description of one or several cases in which no attempt is made to answer specific hypotheses or to compare results with another group of cases
• No control• Classical clinical study• Its value probably under rated
Case Reports and Case Series
Example: investigators at a single institution note that a small number of patients treated with a alternative (complementary) therapy exhibit longer survival and better survival than "expected"
Example: investigators notice a higher than expected incidence of a cancer in a community
Example: investigators note a common occupational exposure in a series of patients with a rare cancer
Case Reports and Case Series
• Problems: lack of a control group no measure of effect no formal statistical analysis
• Advantages: hypotheses generators
Case Series With Literature Controls
• Compare outcomes of case series to "expected" results based on existing records (e.g. published results, national incidence/mortality rates)
• Problems: lack of comparability Confounding
• Healthy Worker Effect Bias
5. Ecologic or trend study :
• Group based study
• Unit of observation is a group eg country, state etc.
Observed effect difficult to interpret at individual level (ecologic fallacy).
Otherwise efficient to do.
5. Ecologic or trend study :
• Group based study, unit of observation is a group e.g. country, state etc.
• Ignore variability between individuals• May ascribe to members characteristics they do
not possess as individuals
Quantity of salt sold at Henan province in China
Age standardized death rate per 1000
Qualitative research :
• Development of concepts which help us to understand social phenomena in natural settings, giving due emphasis to the meanings, experiences, and views of all the participants
• It does not primarily seek to provide quantified answers to research questions
• Particularly useful for explaining complex phenomena not amenable to quantitative research
Qualitative research : - cont
• It has an important role in medical research because health care deals with people and people are more complex than the subjects of the natural sciences.
• There is a whole set of questions about human interaction that we need answers to.
• Obvious areas of application are doctor-patient relationship, treatment compliance, clinical decision making process, issues on health service organisation and policy issues.
Qualitative research-cont’d:
• Development of concepts which help us to understand social phenomena in natural settings, giving due emphasis to the meanings, experiences, and views of all the participants
• Useful for explaining complex phenomena not amenable to quantitative research
• Approaches- Focus group, observation, interview, diary
• Obvious areas of application are doctor-patient relationship, treatment compliance, clinical decision making process, issues on health service organization and policy issues
Conceptia unui plan de cercetare
1. Definitia problemei
2. Dezvoltarea planului de cercetare • Lista elementelor studiului
• Identificarea referintelor publicate
3. Introducerea (fondul problemei) si semnificatia sa (istoric al cercetarilor anterioare, motivatie, importanta)
Plan de studiu
• Problema cercetata• Semnificatie (background)• Designul studiului• Populatia de studiu si
esantionarea• Variabile si masuratori• Elemente statistice
• Aspecte etice• Controlul calitatii si
evaluarea datelor
• Problema principala a studiului?• De ce este important?• Cum se va face studiul ?
• Care sunt subiectii si cum sunt selectati?
• Ce masuri vor fi luate?• Dimensiunea lotului si analiza?• Exista probleme etice?• Cum se asigura controlul calitatii
datelor si analizei acestora?
Fond si semnificatie
• Bazat pe experienta
• Atentie la idei noi
• Atentie la tehnologii noi
• Sa fim constienti despre punctele forte si slabe ale
cercetarilor anterioare similare, proprii sau de
literatura
• Sa stim ce dorim sa comunicam / confirmam la final
Fondul si semnificatia problemei / importanta pentru protocol
• Asemanator cu introducerea la un articol• Introduce cercetarea propusa, in context• Descrie motivatia studiului• Ce se stie despre topic• De ce este problema propusa, importanta?• Ce tip de raspuns asteptam de la studiu?
Fond si semnificatie
• Citarea cercetarilor relevante anterioare (inclusiv propriile date)
• Indica punctele forte si slabe ale studiilor anterioare, ca si intrebarile ramase fara raspuns.
• Arata cum vor fi folosite rezultatele studiului propus pentru rezolvarea neclaritatilor si influentarea politicii de sanatate sau practicii clinice
Gasirea literaturii adecvate
• End note, Reference manager• Verifica formatul referintelor conform
instructiunilor pentru autori si sunt incluse pe masura ce se scrie protocolul
• Se pastreaza copii ale tuturor referintelor• PubMed: www.ncbi.nlm.nih.gov• Comunicari personale (cine si cand)• Date nepublicate (Cel mai bine se evita)
Gasirea literaturii adecvate
• End note, Reference manager• Verifica formatul referintelor conform
instructiunilor pentru autori si sunt incluse pe masura ce se scrie protocolul
• Se pastreaza copii ale tuturor referintelor• PubMed: www.ncbi.nlm.nih.gov• Comunicari personale (cine si cand)• Date nepublicate (Cel mai bine se evita)
Fundamentele Stiintifice ale Cercetarii
• mai multe principii fundamentale sunt utilizate in cercetarea stiintifica: 1.Ordinea
2.Deductia si Sansa
3.Evaluarea si Probabilitatea
4.Ipoteza
Fundamentele Stiintifice ale Cercetarii
• Evaluarea si Probabilitatea(1)
– Cerinta critica a efectuarii
proiectului in cercetare, aceea
care asigura validitatea, este
evaluarea probabilitatiievaluarea probabilitatii de la
inceput pana la capat
Fundamentele Stiintifice ale Cercetarii
Ipoteza
– ipotezele sunt afirmatiiafirmatii atent construite referitoare la un fenomen
intalnit intr-o populatie
– ipotezele pot fi generategenerate fie prin:
• rationament deductivdeductiv
• rationament inductivinductiv rezultat din observatii anterioare
ConcluziiConcluzii
Les sciences sont faites par additions.Nul ne commence ou acheve.Nous sommes montes sur les epaules d’un geant. Nous voyons tot ce que voit le geant, et quelque chose d’avantage.
Guy de Chauliac, 1684