Understanding Medical Articles and Reports Linda Vincent, MPH UCSF Breast SPORE Advocate September 24, 2005 [email protected] 510-527-6720

UnderstandingUnderstanding Medical Articles and Medical Articles and

ReportsReportsLinda Vincent, MPHLinda Vincent, MPH

UCSF Breast SPORE AdvocateUCSF Breast SPORE Advocate

September 24, 2005September 24, 2005

[email protected]@earthlink.net

510-527-6720510-527-6720

Introduction to StatisticsIntroduction to Statistics

Mean, average of a set of numbers or Mean, average of a set of numbers or valuesvalues

Median, the number closest to the Median, the number closest to the middle of a set of numbersmiddle of a set of numbers

Standard Deviation, information on the Standard Deviation, information on the spread of the numbers from a complex spread of the numbers from a complex calculationcalculation

More StatisticsMore Statistics

Probability, p-value, comparing sets of numbers Probability, p-value, comparing sets of numbers from research in another complicated from research in another complicated calculation that gives information on calculation that gives information on statistical statistical significancesignificance p<.05 is the same as 95% Confidence Intervalsp<.05 is the same as 95% Confidence Intervals

Answers question like, how likely is it thatAnswers question like, how likely is it that people in people in the study that got the investigational drug got better the study that got the investigational drug got better because the drug did its job, or whether they got because the drug did its job, or whether they got better due to some other factor.better due to some other factor.

Risk RatioRisk Ratio

Relative Risk or Risk Ratio, RR is used widely in Relative Risk or Risk Ratio, RR is used widely in research papers. Compares the probability research papers. Compares the probability of an outcome among individuals who have a of an outcome among individuals who have a specific “exposure” or a specific characteristic to specific “exposure” or a specific characteristic to those who have not been those who have not been exposedexposed

RR is calculated in Cohort or Experimental RR is calculated in Cohort or Experimental studies (Clinical Trials)studies (Clinical Trials)

Calculating Relative RiskCalculating Relative Risk

2 X 2 Table, see page 51 of Cook Article, Lung2 X 2 Table, see page 51 of Cook Article, Lung

Number Number with with

diseasedisease

Number Number without without diseasedisease

Number of Number of exposedexposed

9090 19,84619,846

Number of Number of unexposedunexposed

115115 19,82719,827

Calculating Relative Risk-2Calculating Relative Risk-2

RR Calculation:RR Calculation:

RR = RR = Absolute risk in exposed participantsAbsolute risk in exposed participants

Absolute risk in unexposed Absolute risk in unexposed participantsparticipants

90/19,93490/19,934 RR = 0.78RR = 0.78

115/19,942115/19,942 CI = 0.59-1.03CI = 0.59-1.03

p-value = .08p-value = .08

Interpretation of RRInterpretation of RR

RR equal to or greater than one, written RR equal to or greater than one, written as =>1 The higher the number above as =>1 The higher the number above one the greater the risk/disease is one the greater the risk/disease is associated with the exposureassociated with the exposure

RR =< 1 There is no association of the RR =< 1 There is no association of the risk/disease to the exposurerisk/disease to the exposure

RR = 1 The risk is the same in both RR = 1 The risk is the same in both groupsgroups

Interpretation of Confidence Interpretation of Confidence IntervalsIntervals

Confidence Intervals, CI Confidence Intervals, CI 95% CI is current standard95% CI is current standard

If the CI does not include 1.0 that the RR is If the CI does not include 1.0 that the RR is statistically significantstatistically significant

Previous example in the Cook article, CI = Previous example in the Cook article, CI = 0.59-1.030.59-1.03

Odds RatiosOdds Ratios

Case-Control Studies can’t use RR because the Case-Control Studies can’t use RR because the OR, Odds Ratios are an estimate of RROR, Odds Ratios are an estimate of RR

Number with Number with disease disease (cases)(cases)

Number Number without without disease disease (controls(controls

Number Number exposedexposed

Number not Number not exposedexposed

Absolute RiskAbsolute Risk

Absolute Risk gives an actual number of Absolute Risk gives an actual number of health problems that happened or were health problems that happened or were prevented due to a drugprevented due to a drug

Doctors and patients have difficulty Doctors and patients have difficulty understanding RR and ORunderstanding RR and OR

Use of NSAIDS and Risk of Breast Use of NSAIDS and Risk of Breast Cancer: The Case-Control Surveillance Cancer: The Case-Control Surveillance

Study RevisitedStudy Revisited

Advantages of Case-Control Studies:Advantages of Case-Control Studies:

Less expensive and time-consuming than Less expensive and time-consuming than cohort studies especially with rare cohort studies especially with rare diseasesdiseases

Odds Ratio can be used to estimate the Odds Ratio can be used to estimate the Risk RatioRisk Ratio



Disadvantages of Case-Control Studies:Disadvantages of Case-Control Studies:

Cases and Controls may come from different Cases and Controls may come from different groups which will bias the resultsgroups which will bias the results

Time-related relationships may be difficult to Time-related relationships may be difficult to ascertainascertain

There is the always the possibility of recall bias There is the always the possibility of recall bias when asking about exposures that occurred in when asking about exposures that occurred in the pastthe past



What is the purpose of the study and what What is the purpose of the study and what question did the authors addressquestion did the authors address??

See first sentences of the abstractSee first sentences of the abstract

What were the unanswered questions raised by What were the unanswered questions raised by prior scientific work that led to this studyprior scientific work that led to this study??

The meta-analysis of Khuder and Mutgi found an The meta-analysis of Khuder and Mutgi found an 18% decreased risk in regular NSAIDs users in 8 18% decreased risk in regular NSAIDs users in 8 case-control studies.case-control studies.

Critical Evaluation of Zhang Article, Critical Evaluation of Zhang Article, ContinuedContinued

Do the authors state a hypothesis? If so what is Do the authors state a hypothesis? If so what is it?it?

Hypothesis is a statement of belief used in the Hypothesis is a statement of belief used in the evaluation of population values. evaluation of population values.

Hypothesis statement: There is an association Hypothesis statement: There is an association between the exposure and the outcome.between the exposure and the outcome.

No hypothesis statement in the Zhang articleNo hypothesis statement in the Zhang article

Zhang, continuedZhang, continued

What are the results?What are the results?Table 1-For the most relevant category, Table 1-For the most relevant category,

regular use of NSAIDs, OR was 0.78, 95% regular use of NSAIDs, OR was 0.78, 95% Confidence Intervals (CI) 0.63-0.97Confidence Intervals (CI) 0.63-0.97

CI dosen’t include 1.0CI dosen’t include 1.0Table 2-Longer duration of regular NSAIDs Table 2-Longer duration of regular NSAIDs

use was associated with a lower risk of use was associated with a lower risk of breast cancer, p-value for trend was 0.02breast cancer, p-value for trend was 0.02

Table 3-Looked at differences between Table 3-Looked at differences between aspirin, Ibuprofen, and NSAIDs (p-value aspirin, Ibuprofen, and NSAIDs (p-value for trend, not significant)for trend, not significant)


What are the conclusions drawn from the What are the conclusions drawn from the results? Are the conclusions supported by results? Are the conclusions supported by evidence in the article?evidence in the article?

First paragraph under DISCUSSION, “Our results First paragraph under DISCUSSION, “Our results suggest a modest decrease in the risk of breast suggest a modest decrease in the risk of breast cancer associated with regular NSAIDs use….”cancer associated with regular NSAIDs use….”

Last paragraph, “In summary, the present study Last paragraph, “In summary, the present study found…the effect is relatively weak. Given the found…the effect is relatively weak. Given the conflicting results from large cohort studies…too conflicting results from large cohort studies…too early to suggest that regular use of NSAIDs early to suggest that regular use of NSAIDs could help prevent breat cancer.”could help prevent breat cancer.”


What methods did the authors use?What methods did the authors use?

Cases were selected from patients living Cases were selected from patients living within one hour driving distance to the within one hour driving distance to the hospitals hospitals

Cases were interviewed by trained nurse Cases were interviewed by trained nurse interviewers using structured interviewers using structured questionnairesquestionnaires

Controls…Controls… Data analysis, relationships of use to risk Data analysis, relationships of use to risk

performed with multiple logistic regression performed with multiple logistic regression models models


What are the strengths of the paper?What are the strengths of the paper?

Researchers/authors attempted to Researchers/authors attempted to validate previous studies on use of validate previous studies on use of NSAIDs and reducing risk of breast NSAIDs and reducing risk of breast cancercancer

Note on biological mechanism for Note on biological mechanism for reducing riskreducing risk

Note on inconsistencies from other Note on inconsistencies from other studiesstudies


Are there obvious problems with the article?Are there obvious problems with the article? The hormone receptor status of the tumors was The hormone receptor status of the tumors was

obtained from only 26% of the cases. Other risk obtained from only 26% of the cases. Other risk factors for breast cancer were not evaluated, but factors for breast cancer were not evaluated, but were similar among cases with data on hormone were similar among cases with data on hormone status suggesting absence of selection biasstatus suggesting absence of selection bias

What additional experiments would strenghten the What additional experiments would strenghten the authors conclusionsauthors conclusions??

Are the findings significant? If so, for who?Are the findings significant? If so, for who?

ResourcesResources

Free subscription servicesFree subscription services BreastCancer.Net, BreastCancer.Net,

http://breastcancer.nethttp://breastcancer.net Amedeo.com, Amedeo.com, http://amedeo.comhttp://amedeo.com Medscape, Medscape,

http://www.medscape.comhttp://www.medscape.com PubCrawler, PubCrawler,

http://pubcrawler.gen.tcd.iehttp://pubcrawler.gen.tcd.ie

Resources continued…Resources continued…

National Cancer InstituteNational Cancer InstitutePub Med, Pub Med, http://pubmed.govhttp://pubmed.govMedLinePlus, MedLinePlus, http://medlineplus.govhttp://medlineplus.gov

FDA Center for Drug Evaluation and ResearchFDA Center for Drug Evaluation and Researchhttp://www.fda.gov/cderhttp://www.fda.gov/cder

GuidelinesGuidelinesNational Comprehensive Cancer Network,National Comprehensive Cancer Network,http://nccn.orghttp://nccn.org

San Antonio Breast Cancer SymposiumSan Antonio Breast Cancer Symposiumhttp://sabcs.orghttp://sabcs.org

American Society of Clinical OncologyAmerican Society of Clinical Oncologyhttp://asco.orghttp://asco.org

Project LEADProject LEAD

http://natlbcc.orghttp://natlbcc.org or Google National or Google National Breast Cancer CoalitionBreast Cancer Coalition

Check left column links, click on Check left column links, click on Education and Training, and click again Education and Training, and click again on Project LEADon Project LEAD

Documents

Understanding Medical Articles and Reports Linda Vincent, MPH UCSF Breast SPORE Advocate September 24, 2005 [email protected] 510-527-6720