實證醫學: 文獻搜尋(PGY, 2010).ppt

2010~2011

2010 PGY

(20)

PICO

: Oxford Centre for EBM Levels of Evidence(1) http://www.cebm.net/index.aspx?o=1047

2 2010.6: http://www.cebm.net/index.aspx?o=5653

LevelTherapy/Prevention, Aetiology/Harm1aSystematic review of RCTs + Meta-Analysis1bRandomized controlled trial (RCT)1cAll-or-none2aSystematic review of cohort studies2bCohort study or poor RCT2cOutcomes research3aSystematic review of case-control studies3bCase-control study4Case series5Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles"

LevelTherapy/Prevention, Aetiology/Harm 1aSystematic review of RCTs + Meta-Analysis 1bRandomized controlled trial (RCT)1cAll-or-none2aSystematic review of cohort studies 2bCohort study or poor RCT2cOutcomes research ; Ecological studies3aSystematic review of case-control studies 3bCase-control study 4Case series5Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles"

all-or- none :

all patients died before the drug became available, but some now survive on it; or

when some patients died before the drug became available, but none now die on it.

Outcomes research is a broad umbrella term without a consistent definition. However it tends to describe research that is concerned with the effectiveness of public-health interventions and health services; that is, the outcomes of these services. Attention is frequently focused on the affected individual with measures such as quality of life and preferences but outcomes research may also refer to effectiveness of health-care delivery, with measures such as cost-effectiveness, health status and disease burden. The present review details the historical background of outcomes research to reveal the origins of its diversity. The value and relevance of outcomes research, commonly employed research techniques and examples of recent publications in the area are also discussed. (Intern Med J 2003; 33: 110118)

WHAT IS OUTCOMES RESEARCH?"Outcomes research" is a term developed in the past 15years to describe clinical research concerning the outcomes of medical care (1, 2). Outcomes, broadly defined, can include any variable used to assess the effect of some medical treatment or intervention. "Outcomes research," however, connotes clinical research that focuses less on physiology or biochemical processes and more on clinical end points directly relevant to patients and society: mortality, quality of life, health status, functional status, and costs of care (3, 4). Outcomes research examines the effectiveness of treatment in real clinical settings of heterogeneous patient populations with barriers to treatment rather than the efficacy of treatment in the more controlled research settings with carefully selected, motivated subjects. In addition, outcomes research is concerned with a broad range of issues touching on all aspects of health care delivery, from the clinical encounter between patient and clinician to questions of the organization, financing, and regulation of the health care system. While large, population-based randomized controlled studies using outcomes important to patients (often called "effectiveness trials") are a type of outcomes research, much of outcomes research relies on observational, nonrandomized designs (5). In fact, outcomes research performed by trainees will likely be observational research because of the time and expense involved in performing effectiveness randomized controlled trials. There is a growing recognition of the need for outcomes research, both observational and experimental, to understand and improve the way health care is delivered throughout our society.

Although the terms "outcomes research," "clinical epidemiology," and "health services research" have overlapping definitions, we use "outcomes research" in a broad way to include much of the disciplines of clinical epidemiology and health services research. Therefore, we define outcomes research as clinical research attempting to understand and improve the outcomes of illness and medical treatment by focusing on those outcomes important to patients and society.

Although it is difficult to draw a sharp line distinguishing outcomes research from other clinical research, many important types of clinical studies are clearly not outcomes studies. For example, small clinical trials using physiologic or biochemical end points are not outcomes research. Nonetheless, faculty performing these other types of clinical research have much to contribute to training outcomes researchers, and trainees interested in other types of clinical research could benefit from many of the tools taught to outcomes researchers.

Pulmonary clinicians have been doing outcomes research for at least 25years. As one example, the Nocturnal Oxygen Therapy Trial in the 1970s used quality of life, as well as survival, as an outcome in a large effectiveness trial to demonstrate the value of oxygen therapy for patients with COPD and hypoxemia (6). The investigators used this study to describe the effect of COPD on the quality of life in these patients (7). Since that time, there has been a large body of work assessing the quality of life and functional status of patients with COPD and asthma and using these measures to determine the effectiveness of treatments (8).

Critical care researchers have been among the leaders in assessing outcomes of medical care and performing risk adjustment to control for severity of illness. The APACHE score was one of the earliest validated systems to assess risk, control for severity of illness, and predict outcome (14), and the APACHE III remains one of the most comprehensive and accurate risk adjustment systems available (15). Assessing outcomes and predictors of outcomes in critical care has been an important and vital area of research for three decades. http://ajrccm.atsjournals.org/cgi/content/full/157/4/1012

http://www.ahrq.gov/clinic/outfact.htm

5: , , , ,

Randomized Controlled Trial (RCT)

SUNY Downstate EBM Tutorial: http://library.downstate.edu/EBM2/research.htm ,

http://www.dartmouth.edu/~biomed/services.htmld/EBP_docs/types_of_studies_downstate.pdf

(Medical Research Council. Streptomycin treatment of pulmonary tuberculosis. BMJ 1948;2:769782.) Ann McKibbonp.24-252008

A randomized controlled study is one in which:

1. There are two groups, one treatment group and one control group. The treatment group receives the treatment under investigation, and the control group receives either no treatment or some standard default treatment.

2. Patients are randomly assigned to all groups.

Assigning patients at random reduces the risk of bias and increases the probability that differences between the groups can be attributed to the treatment.

Having a control group allows us to compare the treatment with alternative choices. For instance, the statement that a particular medication cures 40% of cases tells us very little unless we also know how many cases get better on their own! (Or with a different treatment).

With certain research questions, randomized controlled studies cannot be done for ethical reasons. For instance, it would be unethical to attempt to measure the effect of smoking on health by asking one group to smoke two packs a day and another group to abstain, since the smoking group would be subject to unnecessary harm.

Randomized controlled trials are the standard method of answering questions about the effectiveness of different therapies. If you have a therapy question, first look for a randomized controlled trial, and only go on to look for other types of studies if you don't find one.

Cohort Study



()

(observational study) (the cohort) ( outcome) (:3)

A Cohort Study is a study in which patients who presently have a certain condition and/or receive a particular treatment are followed over time and compared with another group who are not affected by the condition under investigation.

For instance, since a randomized controlled study to test the effect of smoking on health would be unethical, a reasonable alternative would be a study that identifies two groups, a group of people who smoke and a group of people who do not, and follows them forward through time to see what health problems they develop.

Cohort studies are not as reliable as randomized controlled studies, since the two groups may differ in ways other than in the variable under study. For example, if the subjects who smoke tend to have less money than the non-smokers, and thus have less access to health care, that would exaggerate the difference between the two groups.

The main problem with cohort studies, however, is that they can end up taking a very long time, since the researchers have to wait for the conditions of interest to develop. Physicians are, of course, anxious to have meaningful results as soon as possible, but another disadvantage with long studies is that things tend to change over the course of the study. People die, move away, or develop other conditions, new and promising treatments arise, and so on. Even so, cohort studies are generally preferred to case control studies , since they involve far fewer statistical problems and generally produce more reliable answers.

Case Control Study



Case control studies are studies in which patients who already have a certain condition are compared with people who do not.

For example: a study on which lung cancer patients are asked how much they smoked in the past and the answers are compared with a sample of the general population would be a case control study.

Case control studies are less reliable than either randomized controlled trials or cohort studies. Just because there is a statistical relationship between two conditions does not mean that one condition actually caused the other. For instance, lung cancer rates are higher for people without a college education (who tend to smoke more), but that does not mean that someone can reduce his or her cancer risk just by getting a college education.

The main advantages of case control studies are:

They can be done quickly. By asking patients about their past history, researchers can quickly discover effects that otherwise would take many years to show themselves.

Researchers don't need special methods, control groups, etc. They just take the people who show up at their institution with a particular condition and ask them a few questions.

The first study to suggest a new medical conclusion will often be a case control study, perhaps designed to check on a hypothesis suggested by a case series. If possible, researchers will generally try to confirm the results with a randomized controlled trial or a cohort study.

Case Series and Case Report



Case series and case reports consist either of collections of reports on the treatment of individual patients, or of reports on a single patient.

For example: one of your patients has a condition that you have never seen or heard of before and you are uncertain what to do. A search for case series or case reports may reveal information that will assist in a diagnosis. However, for any reasonably well-known condition you should be able to get better evidence. Case series and case reports, since they use no control group with which to compare outcomes, have no statistical validity .

Systematic Review + Meta-Analysis +



(RCT)

Systematic Review

systematic review

Unsystematic narrative review:

reviewer

Important medical questions are typically studied more than once, often by different research teams in different locations.

A systematic review is a comprehensive survey of a topic in which all of the primary studies of the highest level of evidence have been systematically identified, appraised and then summarized according to an explicit and reproducible methodology. A meta-analysis is a survey in which the results of all of the included studies are similar enough statistically that the results are combined and analyzed as if they were one study. In general a good systematic review or meta-analysis will be a better guide to practice than an individual article.

Pitfalls specific to meta-analysis include:

1. It's rare that the results of the different studies precisely agree, and often the number of patients in a single study is not large enough to come up with a decisive conclusion.

2. If the authors are interested in supporting a particular conclusion, they can include studies that support that conclusion and omit studies that do not. Do the authors explain in their paper exactly on what basis they included studies , and do their reasons make sense?

3. Studies that show some kind of positive effect tend to be published more often than those that do not. This means that if the authors include only published studies, several weak positive studies may seem to add up to a strong positive result. Do weak negative studies exist? This effect is known as Publication bias.

PICO, plus , MeSH TermsFIRST: Filtered Resources (EBM Databases)PLUS: Unfiltered Resources (Medline)/(B)(A) (Information bias)

MedlineEMBASEPsyINFOCINAHL

/: Systematic Review (Information bias)

Montori VM, Smieja M, Guyatt GH (2000). Publication bias. Mayo Clin Proc 75:1284-8.

Publication bias.

A, The black circle represents the underlying truth. The white square represents the pooled estimate from a systematic review of all the evidence (small shaded circles).

B, The white circles represent evidence that was not identified by the reviewers because it was not published. Note the error in the pooled estimate (publication bias).

Free

Free

http://library.mmh.org.tw

http://library.mmh.org.tw/EBMR.htm

5S EBM Resources (!)

Model from: Haynes, R. B. (2006). Of studies, syntheses, synopses, summaries, and systems: the "5S" evolution of information services for evidence-based health care decisions. ACP Journal Club, 145(3), A8.

UpToDate

BMJ Clinical Evidence

FirstConsult

ACP PIER

ACP Journal Club, Evidence-Based Medicine

(PubMed, Ovid Medline)

Cochrane Database of Systematic Reviews

Database of Abstracts of Reviews of Effects

(PubMed, Ovid Medline): Systematic Reviews

(PubMed, Ovid Medline, CINAHL, EMBASE

Cochrane CENTRAL, Google Scholar

CEPS, )

3.synopses

4.syntheses

5.studies

1.systems

Filtered

Resources

Unfiltered

Resources

2.summaries

PICO

PPatient/ProblemIInterventionproton pump inhibitorCComparison OOutcomesTypeDiagnosis Therapy Prognosis Harm Etiology

PICO ()

PPatient/Problemgastroesophageal refluxIInterventionPPICComparisonnon-drug therapies OR placebos OROOutcomeshoarsenessTypeDiagnosis Therapy Prognosis Harm Etiology

UpToDate: Search

gastroesophageal reflux PPI hoarseness

(hoarseness)(PPI)(gastroesophageal reflux )(gastro): ANDOR


UpToDate: Result

PPIH2RA

Grade 1 :

Grade A: RCT

Clinical Evidence: Search ()

GERD

Topic

Clinical Evidence: Result

:

Clinical Evidence: Result

Clinical Evidence: GRADE Table

Type of evidence: 4=RCT; 2=Observational

Consistency: similarity of results across studies

Directness: generalisability of population or outcomes Effect size: based on relative risk or odds ratio

4: RCT / SR of RCT

0: (blind, follow up)

0: /

OR/RR/HR

0:

vs. (PubMedMeSH, MeSH Term)

intensive care vs. intensive care

vs.

(PubMedMeSH, MeSH Term)

therap* : therapy , therapeutic , therapeutics

convention*: convention, conventional

vs.

vs. (Google)

"" "" ""

inhibitor

inhibitors

esophageal reflux

gastro-oesophageal reflux

GERD

gastroesophageal reflux

lymph node removal

lymphadenectomy

lymph nodes excision

lymph nodes dissection

(MeSH)

AND OR

OR AND

( OR ) AND

AND

OR

NOT

: AND

AND

: OR

OR

: NOT

NOT

:

AND OR

OR AND

( OR ) AND

:

AND OR ( X )

OR AND ( O )

AND ( OR ) ( O )

4 x ( 2 + 3 )

= AND OR AND

4 x 2 + 4 x 3

Title Keyword Abstract MeSH Term Full Text All Fields

!

: ? ()

: ? (roselle )

translation

translation

database

Medline

queries

Standard

Medical Subject Headings

Free Text

Controlled

Vocabulary

GERD

user

Gastroesophageal Reflux

Gastroesophageal Reflux

articles

authors

vs.

Free text (: summariesGoogle)

User ()

user

initial treatment

=======================================================

Controlled vocabulary (: MeSH: Medical Subject Headings)

()

User

12

/

user

vs. (Free Text) (Controlled Vocabulary)

: Google

: Severe Acute Respiratory Syndrome2003MeSH

: repeated fine-needle aspiration => repeat*

=> (intensive OR tight OR strict) AND glycemic control

=> Roselle vs Roselle

: Medline: MeSHCINAHL Headings

()

/

PubMed: General Search ()

http://www.ncbi.nlm.nih.gov/sites/entrez?holding=itwmmhlib&tool=itwmmhlib&myncbishare=itwmmhlib

PubMed


PubMed: Advance Search ()

(8hr)

#

PubMed: Details

[MeSH Terms]:

[TIAB]: TitleAbstract

[Text Word]: TitleAbstract MeSH termsPublication TypesSubstance NamesPersonal Name

[All Fileds]:

PubMed: Search ()

gastroesophageal reflux AND PPI AND hoarseness


PubMed / Ovid Medicine:

MeSH Term

P I C O

Clinical Queries

ACP J Club Cochrane Reviews

Limits

[major] OR [title] ()

PubMed: MeSH

MeSH TermMeSH Term* MeSH

PPatient/Problemgastroesophageal reflux OR GERD OR esophageal reflux OR gastro-esophageal reflux OR gastro-oesophageal reflux IInterventionPPI OR PPIs OR proton pump inhibitor OR proton pumpsCComparisonnon-drug therapies OR placebos OROOutcomeshoarsenessTypeDiagnosis Therapy Prognosis Harm Etiology

gastroesophageal reflux OR GERD OR esophageal reflux OR gastro-esophageal reflux OR gastro-oesophageal reflux

PPI OR PPIs OR proton pump inhibitor OR proton pumps

hoarseness

PubMed: MeSH

1.

3. MeSH Terms

4. MeSH Database

2. Details

Demo: P

gastroesophageal reflux OR GERD OR GORD OR esophageal reflux OR gastro-esophageal reflux OR gastro-oesophageal reflux

P

PubMed: P I C O


Demo


I


Demo

hoarseness

O

hoarseness

Demo

#2 AND #3 AND #4

PubMed: P I C O

PICO?

P

I

O

P I O

P I

I O

PubMed:

: : hoarseness

atypical manifestations

: : hoarseness

()

hoarsenessGERDatypical symptom

Search #2 AND #3 AND (#4 OR atypical) =165

Search #2 AND #3 AND #4 = 72

PubMed:

MeSH

"proton pumps"

PubMed: ACP, Cochrane

#6

Add to

Search/Preview

AND

#

AND (ACP journal club[Journal]OR "Cochrane database of systematic reviews (Online)"[Journal])

acp...

OR

ACP journal club

#3 ("ACP journal club"[Journal] OR "Cochrane database of systematic reviews (Online)"[Journal])

ACP J Club: 101EBM

PubMed: Clinical Queries

Filter citations to a specific clinical study category and scope. These search filters were developed by Haynes RB et al.

Filter citations for systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine, consensus development conferences, and guidelines. See related sources.

#8

#6

6

99

#8(198)Systematic Reviews#5(24)

(1)

(2) MeSH TermSR

(3) #5

Clinical Queries using Research Methodology Filters

CategoryOptimized ForSensitiveSpecificPubMed Equivalenttherapysensitive/broad99% 70%((clinical[Title/Abstract] AND trial[Title/Abstract]) OR clinical trials[MeSH Terms] OR clinical trial[Publication Type] OR random*[Title/Abstract] OR random allocation[MeSH Terms] OR therapeutic use[MeSH Subheading])specific/ narrow93% 97%(randomized controlled trial[Publication Type] OR (randomized[Title/Abstract] AND controlled[Title/Abstract] AND trial[Title/Abstract])) diagnosissensitive/ broad98%74%(sensitiv*[Title/Abstract] OR sensitivity and specificity[MeSH Terms] OR diagnos*[Title/Abstract] OR diagnosis[MeSH:noexp] OR diagnostic * [MeSH:noexp] OR diagnosis,differential[MeSH:noexp] OR diagnosis[Subheading:noexp])specific/ narrow64%98%(specificity[Title/Abstract])etiologysensitive/ broad93%63%(risk*[Title/Abstract] OR risk*[MeSH:noexp] OR risk *[MeSH:noexp] OR cohort studies[MeSH Terms] OR group*[Text Word])specific/ narrow51%95%((relative[Title/Abstract] AND risk*[Title/Abstract]) OR (relative risk[Text Word]) OR risks[Text Word] OR cohort studies[MeSH:noexp] OR (cohort[Title/Abstract] AND stud*[Title/Abstract]))prognosissensitive/ broad90%80%(incidence[MeSH:noexp] OR mortality[MeSH Terms] OR follow up studies[MeSH:noexp] OR prognos*[Text Word] OR predict*[Text Word] OR course*[Text Word])specific/ narrow52%94%(prognos*[Title/Abstract] OR (first[Title/Abstract] AND episode[Title/Abstract]) OR cohort[Title/Abstract])clinical prediction guidessensitive/ broad96%79%(predict*[tiab] OR predictive value of tests[mh] OR scor*[tiab] OR observ*[tiab] OR observer variation[mh])specific/ narrow54%99%(validation[tiab] OR validate[tiab])

PubMed: Limits

: Limits In process supplied by publisherMedline Medline

#8

Type of Article

PubMed: [major] OR [title]

GERD[majr] OR GERD[ti] OR gastroesophageal reflux[ti]

()


GERD[mesh] OR GERD[ti] OR gastroesophageal reflux[ti]

GERD

PubMed: Search Strategy ()

PICO()

P

I

O

P I O

P I

I O

MeSH /

Limits

Clinical Queries




hoarseness

#2 AND #3 AND #4

#2 AND #3

#3 AND #4

#2 AND #3 AND (#4 OR atypical)

#6 AND ("acp journal club"[Journal] OR "cochrane database of systematic reviews online"[Journal])

PubMed: Filter your results


!

()!

all-or- none :

all patients died before the drug became available, but some now survive on it; or

when some patients died before the drug became available, but none now die on it.

Outcomes research is a broad umbrella term without a consistent definition. However it tends to describe research that is concerned with the effectiveness of public-health interventions and health services; that is, the outcomes of these services. Attention is frequently focused on the affected individual with measures such as quality of life and preferences but outcomes research may also refer to effectiveness of health-care delivery, with measures such as cost-effectiveness, health status and disease burden. The present review details the historical background of outcomes research to reveal the origins of its diversity. The value and relevance of outcomes research, commonly employed research techniques and examples of recent publications in the area are also discussed. (Intern Med J 2003; 33: 110118)

WHAT IS OUTCOMES RESEARCH?"Outcomes research" is a term developed in the past 15years to describe clinical research concerning the outcomes of medical care (1, 2). Outcomes, broadly defined, can include any variable used to assess the effect of some medical treatment or intervention. "Outcomes research," however, connotes clinical research that focuses less on physiology or biochemical processes and more on clinical end points directly relevant to patients and society: mortality, quality of life, health status, functional status, and costs of care (3, 4). Outcomes research examines the effectiveness of treatment in real clinical settings of heterogeneous patient populations with barriers to treatment rather than the efficacy of treatment in the more controlled research settings with carefully selected, motivated subjects. In addition, outcomes research is concerned with a broad range of issues touching on all aspects of health care delivery, from the clinical encounter between patient and clinician to questions of the organization, financing, and regulation of the health care system. While large, population-based randomized controlled studies using outcomes important to patients (often called "effectiveness trials") are a type of outcomes research, much of outcomes research relies on observational, nonrandomized designs (5). In fact, outcomes research performed by trainees will likely be observational research because of the time and expense involved in performing effectiveness randomized controlled trials. There is a growing recognition of the need for outcomes research, both observational and experimental, to understand and improve the way health care is delivered throughout our society.

Although the terms "outcomes research," "clinical epidemiology," and "health services research" have overlapping definitions, we use "outcomes research" in a broad way to include much of the disciplines of clinical epidemiology and health services research. Therefore, we define outcomes research as clinical research attempting to understand and improve the outcomes of illness and medical treatment by focusing on those outcomes important to patients and society.

Although it is difficult to draw a sharp line distinguishing outcomes research from other clinical research, many important types of clinical studies are clearly not outcomes studies. For example, small clinical trials using physiologic or biochemical end points are not outcomes research. Nonetheless, faculty performing these other types of clinical research have much to contribute to training outcomes researchers, and trainees interested in other types of clinical research could benefit from many of the tools taught to outcomes researchers.

Pulmonary clinicians have been doing outcomes research for at least 25years. As one example, the Nocturnal Oxygen Therapy Trial in the 1970s used quality of life, as well as survival, as an outcome in a large effectiveness trial to demonstrate the value of oxygen therapy for patients with COPD and hypoxemia (6). The investigators used this study to describe the effect of COPD on the quality of life in these patients (7). Since that time, there has been a large body of work assessing the quality of life and functional status of patients with COPD and asthma and using these measures to determine the effectiveness of treatments (8).

Critical care researchers have been among the leaders in assessing outcomes of medical care and performing risk adjustment to control for severity of illness. The APACHE score was one of the earliest validated systems to assess risk, control for severity of illness, and predict outcome (14), and the APACHE III remains one of the most comprehensive and accurate risk adjustment systems available (15). Assessing outcomes and predictors of outcomes in critical care has been an important and vital area of research for three decades. http://ajrccm.atsjournals.org/cgi/content/full/157/4/1012

http://www.ahrq.gov/clinic/outfact.htm

5: , , , ,

(Medical Research Council. Streptomycin treatment of pulmonary tuberculosis. BMJ 1948;2:769782.) Ann McKibbonp.24-252008

A randomized controlled study is one in which:

1. There are two groups, one treatment group and one control group. The treatment group receives the treatment under investigation, and the control group receives either no treatment or some standard default treatment.

2. Patients are randomly assigned to all groups.

Assigning patients at random reduces the risk of bias and increases the probability that differences between the groups can be attributed to the treatment.

Having a control group allows us to compare the treatment with alternative choices. For instance, the statement that a particular medication cures 40% of cases tells us very little unless we also know how many cases get better on their own! (Or with a different treatment).

With certain research questions, randomized controlled studies cannot be done for ethical reasons. For instance, it would be unethical to attempt to measure the effect of smoking on health by asking one group to smoke two packs a day and another group to abstain, since the smoking group would be subject to unnecessary harm.

Randomized controlled trials are the standard method of answering questions about the effectiveness of different therapies. If you have a therapy question, first look for a randomized controlled trial, and only go on to look for other types of studies if you don't find one.

(observational study) (the cohort) ( outcome) (:3)

A Cohort Study is a study in which patients who presently have a certain condition and/or receive a particular treatment are followed over time and compared with another group who are not affected by the condition under investigation.

For instance, since a randomized controlled study to test the effect of smoking on health would be unethical, a reasonable alternative would be a study that identifies two groups, a group of people who smoke and a group of people who do not, and follows them forward through time to see what health problems they develop.

Cohort studies are not as reliable as randomized controlled studies, since the two groups may differ in ways other than in the variable under study. For example, if the subjects who smoke tend to have less money than the non-smokers, and thus have less access to health care, that would exaggerate the difference between the two groups.

The main problem with cohort studies, however, is that they can end up taking a very long time, since the researchers have to wait for the conditions of interest to develop. Physicians are, of course, anxious to have meaningful results as soon as possible, but another disadvantage with long studies is that things tend to change over the course of the study. People die, move away, or develop other conditions, new and promising treatments arise, and so on. Even so, cohort studies are generally preferred to case control studies , since they involve far fewer statistical problems and generally produce more reliable answers.

Case control studies are studies in which patients who already have a certain condition are compared with people who do not.

For example: a study on which lung cancer patients are asked how much they smoked in the past and the answers are compared with a sample of the general population would be a case control study.

Case control studies are less reliable than either randomized controlled trials or cohort studies. Just because there is a statistical relationship between two conditions does not mean that one condition actually caused the other. For instance, lung cancer rates are higher for people without a college education (who tend to smoke more), but that does not mean that someone can reduce his or her cancer risk just by getting a college education.

The main advantages of case control studies are:

They can be done quickly. By asking patients about their past history, researchers can quickly discover effects that otherwise would take many years to show themselves.

Researchers don't need special methods, control groups, etc. They just take the people who show up at their institution with a particular condition and ask them a few questions.

The first study to suggest a new medical conclusion will often be a case control study, perhaps designed to check on a hypothesis suggested by a case series. If possible, researchers will generally try to confirm the results with a randomized controlled trial or a cohort study.

Case series and case reports consist either of collections of reports on the treatment of individual patients, or of reports on a single patient.

For example: one of your patients has a condition that you have never seen or heard of before and you are uncertain what to do. A search for case series or case reports may reveal information that will assist in a diagnosis. However, for any reasonably well-known condition you should be able to get better evidence. Case series and case reports, since they use no control group with which to compare outcomes, have no statistical validity .

Important medical questions are typically studied more than once, often by different research teams in different locations.

A systematic review is a comprehensive survey of a topic in which all of the primary studies of the highest level of evidence have been systematically identified, appraised and then summarized according to an explicit and reproducible methodology. A meta-analysis is a survey in which the results of all of the included studies are similar enough statistically that the results are combined and analyzed as if they were one study. In general a good systematic review or meta-analysis will be a better guide to practice than an individual article.

Pitfalls specific to meta-analysis include:

1. It's rare that the results of the different studies precisely agree, and often the number of patients in a single study is not large enough to come up with a decisive conclusion.

2. If the authors are interested in supporting a particular conclusion, they can include studies that support that conclusion and omit studies that do not. Do the authors explain in their paper exactly on what basis they included studies , and do their reasons make sense?

3. Studies that show some kind of positive effect tend to be published more often than those that do not. This means that if the authors include only published studies, several weak positive studies may seem to add up to a strong positive result. Do weak negative studies exist? This effect is known as Publication bias.

MedlineEMBASEPsyINFOCINAHL

/: Systematic Review (Information bias)

Montori VM, Smieja M, Guyatt GH (2000). Publication bias. Mayo Clin Proc 75:1284-8.

Publication bias.

A, The black circle represents the underlying truth. The white square represents the pooled estimate from a systematic review of all the evidence (small shaded circles).

B, The white circles represent evidence that was not identified by the reviewers because it was not published. Note the error in the pooled estimate (publication bias).


PPIH2RA

Grade 1 :

Grade A: RCT

"" "" ""

Free text (: summariesGoogle)

User ()

user

initial treatment

=======================================================

Controlled vocabulary (: MeSH: Medical Subject Headings)

()

User

12

/

user

PubMed





hoarseness



hoarseness

#3 ("ACP journal club"[Journal] OR "Cochrane database of systematic reviews (Online)"[Journal])

#8(198)Systematic Reviews#5(24)

(1)

(2) MeSH TermSR

(3) #5


GERD[mesh] OR GERD[ti] OR gastroesophageal reflux[ti]

GERD




hoarseness

#2 AND #3 AND #4

#2 AND #3

#3 AND #4

#2 AND #3 AND (#4 OR atypical)

#6 AND ("acp journal club"[Journal] OR "cochrane database of systematic reviews online"[Journal])

Documents

實證醫學: 文獻搜尋(PGY, 2010).ppt