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Tipi di Disegno di Studio
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Objectives To understand the difference between
descriptive and analytic studies
To identify the hierarchy of study designs, and the strengths and weakness of each design
To be able to apply different study designs to the same research question
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Obiettivi Comprendere le differenze tra studi
descrittivi e analitici
Identificare la gerarchia di disegni di studio, e le forze e la debolezza di ogni disegno
Essere capaci di applicare diversi disegni di studio alla stessa domanda di ricerca
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Types of Studies
Descriptive Studies
Observational Analytic Studies Cross Sectional studies Case Control studies Cohort studies
Experimental Studies Randomized controlled trials
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Tipi di Studio
Studi Descrittivi
Studi Analitici e di Osservazione Studi Trasversali Studi Caso Controllo Studi di Coorte
Studi Sperimentali Casualizzato prove controllate
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Hierarchy of Study Types
Descriptive•Case report•Case series•Survey
Analytic
Observational•Cross sectional•Case-control•Cohort studies
Experimental•Randomized controlled trials
Strength of evidence for causality between a risk factor and outcome
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Gerarchia dei tipi di studio
Descrittivi•Rapporto di Caso•Serie di Caso•Esame
Analitici
Osservazionali•Trasversali•Caso-Controllo•Studi di Coorte
Sperimentali•Casualizzato prove controllate
Forza dell'evidenza per la causalità tra un fattore di rischio e conseguenza
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Descriptive studies Getting a “lay of the land”
Surveys (NHIS, MCBS) “How many men in the U.S. filled Viagra
prescriptions in 2004?”
Describing a novel phenomena Case reports or case series
Viagra-associated serous macular detachment.
Sildenafil-associated nonarteritic anterior ischemic optic neuropathy.
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Studi Descrittivi Trovando una “disposizione della terra"
Esami (NHIS, MCBS) "Quanti uomini hanno richiesto/avuto nell'U.S.
una prescrizioni di Viagra nel 2004?"
Descrivendo un nuovo fenomeno Casi riportati o serie di casi
Distacco di macular sieroso (distacco della retina) associato al Viagra.
Alterazioni della retina e neuropatia ottico ischemica anteriore non arteriosa
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Descriptive studies Cannot establish causal relationships
Still play an important role in describing trends and generating hypotheses about novel associations
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Studi Descrittivi Non possono stabilire relazioni causali
Possono giocare però un importante ruolo nel descrivere andamenti ed ipotesi generatrici su possibili associazioni di ipotesi
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Analytic Studies Attempt to establish a causal link between
a predictor/risk factor and an outcome.
You are doing an analytic study if you have any of the following words in your research question: greater than, less than, causes, leads to,
compared with, more likely than, associated with, related to, similar to, correlated with
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Studi Analitici Tentano di stabilire un collegamento
causale tra un fattore predittivo/rischio e un effetto/risultato.
Lei sta facendo uno studio analitico se ha una qualsiasi delle seguenti parole nel quesito di ricerca: maggiore di, minore di, causa, conduce a,
confronto con, più probabile che, associato con, riferito a, simile a, correllato con
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Hierarchy of Study Types
Descriptive•Case report•Case series•Survey
Analytic
Observational•Cross sectional•Case-control•Cohort studies
Experimental•Randomized controlled trials
Strength of evidence for causality between a risk factor and outcome
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Research Question
Is the regular consumption of Red Bull associated with improved academic
performance among U.S. medical students?
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Domanda di Ricerca
Il consumo regolare di Red Bull (Toro Rosso)è associato con una migliorata prestazione
accademica fra gli studenti U.S. di medicina?
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Rationale
“functional drink” designed for periods of mental and physical exertion. performance, concentration, memory,
reaction time, vigilance, and emotional balance
Taurine + glucuronolactone + caffeine
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(quale è il supporto logico della ricerca che si vuole fare)
la "bibita funzionale" disegnata per periodi dell'esercizio mentale e fisico. Performance, la concentrazione, memoria,
tempo di reazione, vigilanza, ed equilibrio emotivo/emozionale
Taurina + il glucuronolactone + la caffeina
Base Razionale
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Cross-sectional Study Cross-sectional study of UCSF medical students
taking USMLE Step 2
Questionnaire administered when registering for USMLE 2 Primary predictor: self-report of >3 cans Red Bull per
week for the previous year Covariates: Age, sex, undergraduate university, place
of birth
Outcome: Score on USMLE Step 2
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Studi Trasversali Studio trasversale di studenti in medicina di
UCSF che prendono USMLE Passo 2
Il questionario somministrato al momento della registrazione per USMLE 2 Fattori predittivi primari: più di 3 barattoli di Red Bul
per settimana nell’anno precedente Covariabili : Età, sesso, carriera universitaria, luogo di
nascita
Risultato: Punteggio all’esame di ammissione a USMLE passo 2
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Cross-sectional study: structure
time
USMLE Score
Red Bull consumption
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Studio Trasversale: struttura
Tempo
Risultato/Punteggio di USMLE
Consumo di Red Bull
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Cross-sectional Study: Descriptive value:
How many UCSF medical students drink Red Bull?
What is the age and sex distribution of UCSF medical students who drink Red Bull?
Analytic value: Is there an association between regular Red Bull
consumption and test scores among UCSF med students? Univariate Multivariate (controlling for “confounders”)
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Studi Trasversali:
Valore Descrittivo: Quanti studenti di medicina di UCSF bevono Red Bull? Quale è l'età e la distribuzione per sesso degli
studenti in medicina di UCSF che bevono Red Bull? Valore Analitico:
Qual’è l’associazione tra Red Bull, il suo regolare consumo e i risultati d’esame tra gli studenti di medicina di UCSF? Una sola variabile Più variabili (controllante I fattori di confondimento)
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Cross-sectional Study: Pluses
+ Prevalence (not incidence)
+ Fast/Inexpensive - no waiting!
+ No loss to follow up
+ Associations can be studied
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Studi Trasversali: Vantaggi
+ Prevalenza (non l'Incidenza)
+ Veloce/Poco costoso - nessuna attesa!
+ Nessuna perdita al follow up
+ Le associazioni possono essere studiate
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Measures of association
Disease
Yes No
Risk Facto
r
Yes A B
No C D
Risk ratio (relative risk)
AA + B
CC + D
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Misure dell’Associazione
Malattia
Yes No
Fattori di
Rischio
Yes A B
No C D
Fattori di Rischio (Rischio
Relativo)
AA + B
CC + D
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Cross-sectional study: minuses
time
- Cannot determine causality
USMLE Score
Red Bull consumption
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Studi trasversali: Aspetti negativi
tempo
Non si può determinare la Causalità
USMLE Punteggio
Consumo di Red Bull
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Cross-sectional study: minuses
- Cannot determine causality
- Cannot study rare outcomes
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Studi Trasversali: Aspetti negativi
- Non si può determinare la Causalità
- Non si può usare per malattie rare
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What if you are interested in the rare outcome?
The association between regular Red Bull consumption and… A perfect score on the USMLE – Step 2 Graduating top 1% of the medical school
class Acceptance into a highly selective residency
ANSWER: A Case-Control study
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Che cosa fate se siete interessati ad un effetto raro?
L'associazione tra il regolare consumo di RedBull e… Un risultato perfetto sull'USMLE. Passo 2 Top della graduatoria 1% degli
studenti ????? di scuola medica L'accettazione in una residenza
estremamente selettiva
RISPOSTA: Uno studio Caso-Controllo
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Case-Control Study
Cases: 4th year med students accepted to residency in “highly selective specialty X”.
Controls: 4th year med students who applied but were not accepted.
Predictor: self-reported regular Red Bull consumption Additional covariates (age, sex, medical school,
undergraduate institution)
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Studio Caso-Controllo
Casi : 4 anni studenti medicina hanno accettato la residenza in “highly selective specialty X”.(specializzazione X altamente selettiva)
Controlli: 4 anni studenti che hanno fattp domanda ma non sono stati accettati.
Predittivo: il consumo regolare di Red Bull Addizionali covariate (età sesso, scuola di medicina
precedente)
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Case control studies
Investigator works “backward” (from outcome to predictor)
Sample chosen on the basis of outcome (cases), plus comparison group (controls)
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Studi caso controllo
Il ricercatore lavora all’indietro (dall’effetto al fattore di rischio)
Il campione è scelto sulla base dell’effetto (casi), più un gruppo di confronto (controlli)
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Case-control study structure
time
ACTUAL CASES4th year UCSF students who matched in “highly
selective specialty X”
ACTUAL CONTROLS4th year students who failed to match in “highly selective
specialty X”
Red Bull consumptionYES
Red Bull consumptionNO
presentpast years
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Strutture dei casi controllo
tempo
ACTUAL CASESStudenti per la selezione
specialità X
ACTUAL CONTROLSStudenti respinti
consumatori Red BullYES
consumatori Red BullNO
presenteAnni precedenti
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Case control studies Determines the strength of the association
between each predictor variable and the presence or absence of disease
Cannot yield estimates of incidence or prevalence of disease in the population (why?)
Odds Ratio is statistics
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Studi casi controllo Misurano la forza dell’associazione tra
ciascuna variabile predittiva e la presenza o assenza di effetto (malattia)
Non possono invece stimare l’incidenza o la prevalenza di effetto (malattia) nella popolazione ( perchè?) non sono un campione rappresentativo della popolazione
La forza dell’associazione viene misurata dal Odds Ratio (rapporto di disparità)
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Case-control Study: pluses
+ Rare outcome/Long latent period
+ Inexpensive and efficient: may be only feasible option
+ Establishes association (Odds ratio)
+ Useful for generating hypotheses (multiple risk factors can be explored)
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studi casi controllo:aspetti positivi
+ studia malattie rare/periodi di latenza lunghi
+ poco costoso ed efficente: può essere l’unica opzione praticabile
+ verifica e misura una associazione(odds ratio)
+ e’ utile per generare delle ipotesi (possono essere esplorati molteplici fattori di rischio)
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Case-control study-minuses
- Causality still difficult to establish
- Selection bias (appropriate controls)
- Recall bias: (retrospective observation)
- Cannot tell about incidence or prevalence
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Studi caso controllo:aspetti negativi
- La casualità rimane difficile da stabilire
- Problemi di selezione (controlli appropriati)
- Problemi di ricordo: (osservazioni retrospettive)
- Non può dire niente su incidenza o prevalenza
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Measures of association
Disease
Yes No
TestYes A B
No C D
Odds ratio (relative risk)
A * D_______
B * C
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Misure di associazione
Effetto/malattia
Yes No
TestYes A B
No C D
Odds ratio (relative risk)
A * D_______
B * C
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Cohort Study All entering medical students surveyed regarding
beverage consumption and variety of other potential covariates
Survey updated annually to record changes in Red Bull consumption
Outcomes: USMLE Step 1 score, USMLE Step 2 score, match in first choice residency
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Studi di coorte Tutte le matricole di medicina sono state
interrogate sul consumo di Red Bul e una quantità di altre covariate
Annualmente è stato aggiornato lo studio registrando i cambiamenti nel consumo di Red Bul
effetti: punteggi per l’ammissione allo step 1 e per lo step 2, appaiamento nella prima amissione alla specializzazione
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Cohortes studies• A cohort (follow-up, longitudinal) study is a
comparative, observational study in which subjects are grouped by their exposure status, i.e., whether or not the subject was exposed to a suspected risk factor
• The subjects, exposed and unexposed to the risk factor, are followed forward in time to determine if one or more new outcomes (diseases) occur• Subjects should not have outcome variable on entry• No new subjects allowed in after initial recruitment
• The rates of disease incidence among the exposed and unexposed groups are determined and compared.
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Studi di coorte• Una coorte (follow-up, longitudinale) è uno studio
comparativo, studio osservazionale nel quale il soggetto è raggruppato a seconda dello stato di esposizione, i.e., se I soggetti sono stati o no esposti ad un fattore di rischio
• I soggetti, esposti e non esposti ad un fattore di rischio sono seguenti in avanti nel tempo se uno o più nuovi effetti compaiono• I soggetti non dovrebbero avere l’effetto/malattia nel
momento dell’entrata (dello studio)• Non possono entrare nuovi soggetti dopo il reclutamento
iniziale (la coorte è chiusa)
• I tassi di incidenza degli effetti/malattia dai gruppi esposti e non esposti saranno misurati e confrontati
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Elements of a cohort study
Selection of sample from population Measures predictor variables in sample Follow population for period of time Measure outcome variable
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Elementi di studio di coorte
Selezione di un campione della popolazione Misura delle variabili predittive nel campione Si segue la popolazione per un periodo di
tempo Misura variabile di effetto
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time
The present The future
Top USMLE scorers
Everyone else
Prospective cohort study structure
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tempo
Presente Futuro
Persone con I punteggi più alti (per l’ammissione)
Anche qualcun’altro
Prospettive delle stutture degli studi di coorte
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Strengths of cohort studies Know that predictor variable was present before
outcome variable occurred (some evidence of causality)
Directly measure incidence of a disease outcome
Can study multiple outcomes of a single exposure (RR is measure of association)
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Punti di forza degli studi di coorte Sapere che la variabile predittiva era presente
prima della comparsa della variabile di effetto (prova di cusalità)
Si può fare la misura diretta dell’incidenza
Posso studiare molti effetti di una singola esposizione (rischi relativo è la misura dell’associazione)
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Weaknesses of cohort studies Expensive and inefficient for studying rare
outcomes Often need long follow-up period or a very large
population Loss to follow-up can affect validity of findings
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Debolezza degli studi di coorte Costosi ed inefficenti per studiare
effetti/malattie rare Spesso sono necessari lunghi periodi di follow –
up o grandissime popolazioni I persi al follow-up possono incidere
negativamente sulla validità dei risultati
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Other types of cohort studies Retrospective cohort
Identification of cohort, measurement of predictor variables, follow-up and measurement of outcomes have all occurred in the past
Much less costly than prospective cohorts Investigator has minimal control over study
design
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Altri tipi di studi di coorte Studio retrospettivo
Identificazione,della coorte misurazione e predizione delle variabili follow-up e misurazione degli effetti che si sono verificati nel passato
Molto meno costoso che la coorte prospettica
L’investigatore ha un minimo controllo sul disegno dello studio (quello che c’è c’è)
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Time in the Cohort Study
Exposed subjects
Unexposed subjects
Classic (Concurrent) Cohort Study
Disease
Disease
Today + 5- 5- 10 + 10
Historical (Non-concurrent) Cohort Study
Exposed subjects
Unexposed subjects
Disease
Disease
Time in Years
Today + 5- 5- 10 + 10
Time in Years
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Tempo nello studio di coorte
Soggetti Esposti
Soggetti Non esposti
Studio classico di coorte (Concurrent)
Effetto/Malattia
Effetto/Malattia
oggi + 5- 5- 10 + 10
storico retrospettivo Cohort Study
Soggetti esposti
Soggetti non esposti
Effetto/Malattia
Effetto/Malattia
Time in Years
oggi + 5- 5- 10 + 10
tempo in anni
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Time in the Cohort Study
d = Disease
Exposed subjects
Unexposed subjects
Today
Time in Years
+ 5- 5- 10 + 10
d
d
d
d
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Tempo nello studio di coorte
d = effetto/malattia
Soggetti Esposti
Soggetti non Esposti
oggi
Tempo in Anni
+ 5- 5- 10 + 10
d
d
d
d
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Measures of Risk
DEPENDENT VARIABLE (disease)
INDEPENDENT VARIABLE (risk factor)
Exposed
With Without
Unexposed
a b
c d
a + c b + d
a + b
c + d
Incidence: a
a + b ; c
c + d
a
Relative risk: a + bc
c + d
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Misura del rischio
Variabile dipendente (effetto/malattia)
VARIABILE INDIPENDENTE (Fattore di Rischio)
Esposti
Con Senza
Non Esposti
a b
c d
a + c b + d
a + b
c + d
Incidenza: a
a + b ; c
c + d
a
Rischio Relativo: a + bc
c + d
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Other types of cohort studies Nested case-control study
Case-control study embedded in a cohort study Controls are drawn randomly from study sample
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Un altro tipo di studio di coorte Studio casi controllo annidato
Studi caso controllo formati (arruolati) in uno studio di coorte
I controlli sono tratti in maniera casuale dall’intera coorte