These annotated slides will help you interpret an OR or RR in clinical terms. Please download these slides and view them in PowerPoint so you can view the annotations describing each slide.
Common measures of association in medical research (UPDATED) 2013Pat Barlow
This is an updated version of my Common Measures of Association presentation. I've updated it to include (1) more detail on rates, risks, and proportions, (2) Absolute Risk Reduction (ARR), Attributable Risk (AR), Number Needed to Treat (NNT) and Number Needed to Harm (NNH). Feel free to email me for a full version of the slideshow.
These annotated slides will help you interpret an OR or RR in clinical terms. Please download these slides and view them in PowerPoint so you can view the annotations describing each slide.
Common measures of association in medical research (UPDATED) 2013Pat Barlow
This is an updated version of my Common Measures of Association presentation. I've updated it to include (1) more detail on rates, risks, and proportions, (2) Absolute Risk Reduction (ARR), Attributable Risk (AR), Number Needed to Treat (NNT) and Number Needed to Harm (NNH). Feel free to email me for a full version of the slideshow.
Mathematics in Epidemiology and Biostatistics (Medical Booklet Series by Dr. ...Dr. Aryan (Anish Dhakal)
Basic mathematics needed for epidemiology and bio statistics. Slides include formulas and conceptual understanding of sensitivity, specificity, predictive values, likelihood ratios, odds, probability and many more.
Lecture on causal inference to the pediatric hematology/oncology fellows at Texas Children's hospital as part of their Biostatistics for Busy Clinicians lecture seriers.
In order to understand medical statistics, you have to learn the very basic concepts as mean, median, and standard deviation. interpretation and understanding of clinical study results depends mainly on statistical background.
How to combine results from randomised clinical trials on the additive scale with real world data to provide predictions on the clinically relevant scale for individual patients
When estimating sample sizes for clinical trials there are several different views that might be taken as to what definition and meaning should be given to the sought-for treatment effect. However, if the concept of a ‘minimally important difference’ (MID) does have relevance to interpreting clinical trials (which can be disputed) then its value cannot be the same as the ‘clinically relevant difference’ (CRD) that would be used for planning them.
A doubly pernicious use of the MID is as a means of classifying patients as responders and non-responders. Not only does such an analysis lead to an increase in the necessary sample size but it misleads trialists into making causal distinctions that the data cannot support and has been responsible for exaggerating the scope for personalised medicine.
In this talk these statistical points will be explained using a minimum of technical detail.
Sample size determination in clinical trials is considered from various ethical and practical perspectives. It is concluded that cost is a missing dimension and that the value of information is key.
Aplicación de Primeros Auxilios Psicológicos a una poblacion diana afectadaGriselda Varela
Los Primeros Auxilios Psicológicos (PAP) son fases prácticas de intervenciones después de un suceso crítico por proveedores certificados y/o organizaciones de auxilio ante las reacciones tempranas de una crisis o situación de emergencia.
El presente expone un escenario donde se aplican las fases de los PAP; se detalla e identifica la población diana afectada, se detecta el grado de afectación, se reconocen las necesidades, se da una posible evolución y describen pautas psicoeducativas para ayudar y orientar a la población afectada.
Mathematics in Epidemiology and Biostatistics (Medical Booklet Series by Dr. ...Dr. Aryan (Anish Dhakal)
Basic mathematics needed for epidemiology and bio statistics. Slides include formulas and conceptual understanding of sensitivity, specificity, predictive values, likelihood ratios, odds, probability and many more.
Lecture on causal inference to the pediatric hematology/oncology fellows at Texas Children's hospital as part of their Biostatistics for Busy Clinicians lecture seriers.
In order to understand medical statistics, you have to learn the very basic concepts as mean, median, and standard deviation. interpretation and understanding of clinical study results depends mainly on statistical background.
How to combine results from randomised clinical trials on the additive scale with real world data to provide predictions on the clinically relevant scale for individual patients
When estimating sample sizes for clinical trials there are several different views that might be taken as to what definition and meaning should be given to the sought-for treatment effect. However, if the concept of a ‘minimally important difference’ (MID) does have relevance to interpreting clinical trials (which can be disputed) then its value cannot be the same as the ‘clinically relevant difference’ (CRD) that would be used for planning them.
A doubly pernicious use of the MID is as a means of classifying patients as responders and non-responders. Not only does such an analysis lead to an increase in the necessary sample size but it misleads trialists into making causal distinctions that the data cannot support and has been responsible for exaggerating the scope for personalised medicine.
In this talk these statistical points will be explained using a minimum of technical detail.
Sample size determination in clinical trials is considered from various ethical and practical perspectives. It is concluded that cost is a missing dimension and that the value of information is key.
Aplicación de Primeros Auxilios Psicológicos a una poblacion diana afectadaGriselda Varela
Los Primeros Auxilios Psicológicos (PAP) son fases prácticas de intervenciones después de un suceso crítico por proveedores certificados y/o organizaciones de auxilio ante las reacciones tempranas de una crisis o situación de emergencia.
El presente expone un escenario donde se aplican las fases de los PAP; se detalla e identifica la población diana afectada, se detecta el grado de afectación, se reconocen las necesidades, se da una posible evolución y describen pautas psicoeducativas para ayudar y orientar a la población afectada.
Mutagenesis is the process by which the genetic information
of an organism is changed in a stable manner.
The term ‘mutation breeding’ has become popular as it
draws attention to deliberate efforts of breeders and
the specific techniques they have used in creating and
harnessing desired variation in developing elite breeding
lines and cultivated varieties.
RNA- A polymer of ribonucleotides, is a single stranded structure. There are three major types of RNA- m RNA,t RNA and r RNA. Besides that there are small nuclear,micro RNAs, small interfering and heterogeneous RNAs. Each of them has a specific structure and performs a specific function.
Epidemiological Approaches for Evaluation of diagnostic tests.pptxBhoj Raj Singh
Diagnosis of a disease or a problem is the first step towards solution/ treatment. Clinical Diagnosis or Provisional Diagnosis is the first step in diagnosis and is done after a physical examination of the patient by a clinician. Clinical diagnosis may or may not be true and to reach Final diagnosis Laboratory Investigations using gross and microscopic pathological observations and determining the disease indicators are required. The diagnostic tests may be Non-dichotomous Diagnostic Tests (when continuous values are given by the test in a range starting from sub-normal to above-normal range) and Dichotomous Diagnostic Tests (when results are given either plus or minus, disease or no-disease). To make non- Dichotomous diagnostic test a Dichotomous one you need to establish the cut-off values based on reference values or Gold Standard test readings or with the use of Receiver operator characteristic (ROC) curves, Precision-Recall Curves, Likelihood Ratios, etc., and finally establishing statistical agreement (using Kappa values, Level of Agreement, χ2 Statistics) between the true diagnosis and laboratory diagnosis. Thereafter, the Accuracy, Precision, Bias, Sensitivity, Specificity, Positive Predictive value, and Negative Predictive value, of a diagnostic test are established for use in clinical practice. Diagnostic tests are also used to determine Prevalence (True prevalence, apparent prevalence) and Incidence of the disease to estimate the disease burden so that control measures can be implemented. There are several Phases in the development and use of a diagnostic assay starting from conceptualization of the diagnostic test, development and evaluation to determine flaws in diagnostic test use and Interpretation influencers. This presentation mainly deals with the epidemiological evaluation procedures for diagnostic tests.
Sensitivity, specificity and likelihood ratiosChew Keng Sheng
A short tutorial on sensitivity, specificity and likelihood ratios. In this presentation, I demonstrate why likelihood ratios are better parameters compared to sensitivity and specificity in real world setting.
Biostatistics are widely used in clinical trials to collect and organize and describe and interpret these result and then give to us proves to take appropriate clinical decisions
Perioperative management of patients on corticosteroidsTerry Shaneyfelt
In these annotated PowerPoints I discuss the evaluation and perioperative management of patient taking or who have taken steroids. I discuss how to determine if the adrenal axis is suppressed and how to provide supplemental glucocorticoids if needed. Remember to download these slides to see the annotations for each slide.
Perioperative Management of Hypothyroid Patients Undergoing Nonthyroidal SurgeryTerry Shaneyfelt
In these annotated PowerPoint slides I describe the perioperative evaluation and management of patients with hypothyroidism needing nonthyroid surgery. Remember to download these slides to view the annotations for each slide.
Perioperative Diabetes Management in Patients on InsulinTerry Shaneyfelt
In these annotated PowerPoints I discuss the control of diabetes in the perioperative period in patients taking insulin. Please download these slides and view them in PowerPoint so you can view the annotations describing each slide.
In these powerpoints I describe how to control glycemia in the perioperative period in patient with diabetes not taking insulin. Please download these slides and view them in PowerPoint so you can view the annotations describing each slide.
Preoperative evaluation of patients with diabetesTerry Shaneyfelt
In these annotated slides I discuss the things you need to consider in the preoperative evaluation of patients with diabetes. This sets the stage for perioperative management of diabetes. Please download these slides and view them in PowerPoint so you can view the annotations describing each slide.
Preoperative evaluation of adults with sleep apneaTerry Shaneyfelt
Patients with sleep apnea present unique challenges in the perioperative period. Over half of patients with sleep apnea are undiagnosed at the time of surgery. I review how to assess risk in patients with suspected or confirmed sleep apnea.
Gupta indices for postop pulmonary complicationsTerry Shaneyfelt
Gupta and colleagues developed 2 prediction rules that can be used to estimate a patient's risk for postoperative pneumonia or respiratory failure. I also review an older prediction rule and show how it compares to the Gupta rules.
In these slides I discuss what to do with the patient post stent who needs noncardiac surgery and I discuss what to do with anti-platelet therapy in the perioperative period. Watch my YouTube description of these slides at http://youtu.be/z8Okm3_GFbU.
Reducing Perioperative Cardiac Risk: Do Beta blockers Help?Terry Shaneyfelt
Review of the effect of beta blockers on perioperative cardiac events including updated recommendations by the ACC/AHA (August 2014. Watch my YouTube video (http://youtu.be/WPLXDm9Nzoc) describing these slides.
Review of 2 metaanalyses of RCTs on the effects of statins in the perioperative period. Watch my YouTube video describing these slides: http://youtu.be/wHYlf26AH00
Who needs preoperative noninvasive cardiac testingTerry Shaneyfelt
Review of recommendations on noninvasive cardiac testing prior to noncardiac surgery. Watch my YouTube video describing these slides: http://youtu.be/lDRUrx45pMw
Overview of preoperative cardiac risk assessmentTerry Shaneyfelt
Basic principles of assessing cardiac risk in patients undergoing noncardiac surgery. Audience: general internists and family practitioners. Watch my YouTube video describing these slides: http://youtu.be/AAGgwU0uXj0
Explore our infographic on 'Essential Metrics for Palliative Care Management' which highlights key performance indicators crucial for enhancing the quality and efficiency of palliative care services.
This visual guide breaks down important metrics across four categories: Patient-Centered Metrics, Care Efficiency Metrics, Quality of Life Metrics, and Staff Metrics. Each section is designed to help healthcare professionals monitor and improve care delivery for patients facing serious illnesses. Understand how to implement these metrics in your palliative care practices for better outcomes and higher satisfaction levels.
ICH Guidelines for Pharmacovigilance.pdfNEHA GUPTA
The "ICH Guidelines for Pharmacovigilance" PDF provides a comprehensive overview of the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines related to pharmacovigilance. These guidelines aim to ensure that drugs are safe and effective for patients by monitoring and assessing adverse effects, ensuring proper reporting systems, and improving risk management practices. The document is essential for professionals in the pharmaceutical industry, regulatory authorities, and healthcare providers, offering detailed procedures and standards for pharmacovigilance activities to enhance drug safety and protect public health.
Health Education on prevention of hypertensionRadhika kulvi
Hypertension is a chronic condition of concern due to its role in the causation of coronary heart diseases. Hypertension is a worldwide epidemic and important risk factor for coronary artery disease, stroke and renal diseases. Blood pressure is the force exerted by the blood against the walls of the blood vessels and is sufficient to maintain tissue perfusion during activity and rest. Hypertension is sustained elevation of BP. In adults, HTN exists when systolic blood pressure is equal to or greater than 140mmHg or diastolic BP is equal to or greater than 90mmHg. The
Global launch of the Healthy Ageing and Prevention Index 2nd wave – alongside...ILC- UK
The Healthy Ageing and Prevention Index is an online tool created by ILC that ranks countries on six metrics including, life span, health span, work span, income, environmental performance, and happiness. The Index helps us understand how well countries have adapted to longevity and inform decision makers on what must be done to maximise the economic benefits that comes with living well for longer.
Alongside the 77th World Health Assembly in Geneva on 28 May 2024, we launched the second version of our Index, allowing us to track progress and give new insights into what needs to be done to keep populations healthier for longer.
The speakers included:
Professor Orazio Schillaci, Minister of Health, Italy
Dr Hans Groth, Chairman of the Board, World Demographic & Ageing Forum
Professor Ilona Kickbusch, Founder and Chair, Global Health Centre, Geneva Graduate Institute and co-chair, World Health Summit Council
Dr Natasha Azzopardi Muscat, Director, Country Health Policies and Systems Division, World Health Organisation EURO
Dr Marta Lomazzi, Executive Manager, World Federation of Public Health Associations
Dr Shyam Bishen, Head, Centre for Health and Healthcare and Member of the Executive Committee, World Economic Forum
Dr Karin Tegmark Wisell, Director General, Public Health Agency of Sweden
CHAPTER 1 SEMESTER V PREVENTIVE-PEDIATRICS.pdfSachin Sharma
This content provides an overview of preventive pediatrics. It defines preventive pediatrics as preventing disease and promoting children's physical, mental, and social well-being to achieve positive health. It discusses antenatal, postnatal, and social preventive pediatrics. It also covers various child health programs like immunization, breastfeeding, ICDS, and the roles of organizations like WHO, UNICEF, and nurses in preventive pediatrics.
Navigating Challenges: Mental Health, Legislation, and the Prison System in B...Guillermo Rivera
This conference will delve into the intricate intersections between mental health, legal frameworks, and the prison system in Bolivia. It aims to provide a comprehensive overview of the current challenges faced by mental health professionals working within the legislative and correctional landscapes. Topics of discussion will include the prevalence and impact of mental health issues among the incarcerated population, the effectiveness of existing mental health policies and legislation, and potential reforms to enhance the mental health support system within prisons.
CRISPR-Cas9, a revolutionary gene-editing tool, holds immense potential to reshape medicine, agriculture, and our understanding of life. But like any powerful tool, it comes with ethical considerations.
Unveiling CRISPR: This naturally occurring bacterial defense system (crRNA & Cas9 protein) fights viruses. Scientists repurposed it for precise gene editing (correction, deletion, insertion) by targeting specific DNA sequences.
The Promise: CRISPR offers exciting possibilities:
Gene Therapy: Correcting genetic diseases like cystic fibrosis.
Agriculture: Engineering crops resistant to pests and harsh environments.
Research: Studying gene function to unlock new knowledge.
The Peril: Ethical concerns demand attention:
Off-target Effects: Unintended DNA edits can have unforeseen consequences.
Eugenics: Misusing CRISPR for designer babies raises social and ethical questions.
Equity: High costs could limit access to this potentially life-saving technology.
The Path Forward: Responsible development is crucial:
International Collaboration: Clear guidelines are needed for research and human trials.
Public Education: Open discussions ensure informed decisions about CRISPR.
Prioritize Safety and Ethics: Safety and ethical principles must be paramount.
CRISPR offers a powerful tool for a better future, but responsible development and addressing ethical concerns are essential. By prioritizing safety, fostering open dialogue, and ensuring equitable access, we can harness CRISPR's power for the benefit of all. (2998 characters)
R3 Stem Cells and Kidney Repair A New Horizon in Nephrology.pptxR3 Stem Cell
R3 Stem Cells and Kidney Repair: A New Horizon in Nephrology" explores groundbreaking advancements in the use of R3 stem cells for kidney disease treatment. This insightful piece delves into the potential of these cells to regenerate damaged kidney tissue, offering new hope for patients and reshaping the future of nephrology.
Defecation
Normal defecation begins with movement in the left colon, moving stool toward the anus. When stool reaches the rectum, the distention causes relaxation of the internal sphincter and an awareness of the need to defecate. At the time of defecation, the external sphincter relaxes, and abdominal muscles contract, increasing intrarectal pressure and forcing the stool out
The Valsalva maneuver exerts pressure to expel faeces through a voluntary contraction of the abdominal muscles while maintaining forced expiration against a closed airway. Patients with cardiovascular disease, glaucoma, increased intracranial pressure, or a new surgical wound are at greater risk for cardiac dysrhythmias and elevated blood pressure with the Valsalva maneuver and need to avoid straining to pass the stool.
Normal defecation is painless, resulting in passage of soft, formed stool
CONSTIPATION
Constipation is a symptom, not a disease. Improper diet, reduced fluid intake, lack of exercise, and certain medications can cause constipation. For example, patients receiving opiates for pain after surgery often require a stool softener or laxative to prevent constipation. The signs of constipation include infrequent bowel movements (less than every 3 days), difficulty passing stools, excessive straining, inability to defecate at will, and hard feaces
IMPACTION
Fecal impaction results from unrelieved constipation. It is a collection of hardened feces wedged in the rectum that a person cannot expel. In cases of severe impaction the mass extends up into the sigmoid colon.
DIARRHEA
Diarrhea is an increase in the number of stools and the passage of liquid, unformed feces. It is associated with disorders affecting digestion, absorption, and secretion in the GI tract. Intestinal contents pass through the small and large intestine too quickly to allow for the usual absorption of fluid and nutrients. Irritation within the colon results in increased mucus secretion. As a result, feces become watery, and the patient is unable to control the urge to defecate. Normally an anal bag is safe and effective in long-term treatment of patients with fecal incontinence at home, in hospice, or in the hospital. Fecal incontinence is expensive and a potentially dangerous condition in terms of contamination and risk of skin ulceration
HEMORRHOIDS
Hemorrhoids are dilated, engorged veins in the lining of the rectum. They are either external or internal.
FLATULENCE
As gas accumulates in the lumen of the intestines, the bowel wall stretches and distends (flatulence). It is a common cause of abdominal fullness, pain, and cramping. Normally intestinal gas escapes through the mouth (belching) or the anus (passing of flatus)
FECAL INCONTINENCE
Fecal incontinence is the inability to control passage of feces and gas from the anus. Incontinence harms a patient’s body image
PREPARATION AND GIVING OF LAXATIVESACCORDING TO POTTER AND PERRY,
An enema is the instillation of a solution into the rectum and sig
UAB Pulmonary board review study design and statistical principles
1. Terry Shaneyfelt, MD, MPH
UAB Division of General Internal Medicine
@EBMTeacher
EBMTeacher.com
UABEBMcourse
YouTube logo image credit (CC0): http://commons.wikimedia.org/wiki/File:Youtube.svg
2. Topics to be covered
Diagnostic testing
Choosing a test and interpreting studies
Randomized controlled trials
Randomization, power, types 1 and 2 errors,
outcome measures
Observational studies
Study design, RR, OR
Screening
Outcomes and biases
3.
4. Diagnostic Testing
Choosing a test
Sensitivity, specificity, likelihood ratios
SpPin and SnNout
Interpreting the results of a diagnostic test
study
Positive and negative predictive values
5. What is the role of testing?
Rule in with high pretest probability
Rule out with low pretest probability
7. Rule in with specific tests
Rule out with sensitive tests
SpPin ( A specific test, if positive, rules in
disease in a high risk person)
SnNout (A sensitive test, if negative, rules out
disease in a low risk person)
Alternatively: Choose test with highest positive
LR (to rule in) and/or lowest negative LR (to rule
out)
Sensitivity Specificity LR + LR -
Test A 95% 80% 4.75 0.06
Test B 90% 90% 9 0.11
Test C 70% 95% 14 0.32
8. To learn more watch my other
videos
Sensitivity: http://bit.ly/1FOlqry
Specificity: http://bit.ly/1IYjv2A
LR: http://bit.ly/1JOofZz
9. CTA High Pretest
Probability
Intermediate
Low Pretest
Probability
Positive
Predictive Value
(%)
96 92 58
Negative
Predictive Value
(%)
60 89 96
Adapted from Table 5 PIOPED II (NEJM 2006;354:2317)
Sens 83%
Spec 96%
10. To learn more watch my other
videos
PPV: http://bit.ly/1HDXWpm
NPV: http://bit.ly/1Faegbq
11.
12. RCTs
Study design
Randomization
Power, type 2 error, and sample size
p-values and type I error
Outcome measures
RRR, ARR, HR, NNT
13. Image from PrevMedFellow (CC A SA license): http://commons.wikimedia.org/wiki/File:Flowchart_of_Phases_of_Parallel_Randomized_Trial_-
_Modified_from_CONSORT_2010.png
Control
14. What do you think is the greatest
risk of bias in a therapy study?
A. Failure to randomize
B. Failure to conceal allocation
C. Failure to blind participants and study
personnel
D. Failure to use intention to treat
analysis
E. Failure to treat groups equally except
for the intervention
15. 2 Reasons:
1. Reduces selection bias
2. Equally distributes prognostic factors
(both known and unknown)
Why Is Randomization So
Important?
The validity of a clinical trial depends on treated &
control patients being prognostically equal, other than
the intervention being tested
16. TRUTH
Difference No difference
Study
Conclusion
Difference
No difference
Beta/
Type II
error
Alpha/
Type I
error
We estimated that with enrollment of 1130 subjects, the study would have 90% power
to show a significant difference between the two groups in the time to the first acute
exacerbation of COPD, assuming that 50% of the participants in the control group
and 40% in the azithromycin group would have an acute exacerbation, that the rate of
nonadherence would be 20%, and that 6% of participants would die or be lost to
follow-up during the study, with a two-sided type I error of 0.05.
Azithromycin for Prevention of Exacerbations of COPD NEJM 2011;365:689
Power
17. Power (greater the desired power the
greater the sample size)
Estimated difference between groups
(smaller the difference the greater the
sample size)
Type 1 error rate (usually 0.05 but the
smaller the greater the sample size)
Variability in the measurements made
within each comparison group (greater
the variability the greater the sample size)
Sample size is affected by…
18. Time to event data is often displayed
as a Kaplan-Meier curve
From N Engl J Med 2011; 365:689-698
19. Azithromycin
(# of events)
Placebo
(# of events)
Hazard Ratio
(95% CI)
p-value
Hospitalization
related to
COPD
156 200
0.82
(0.64 - 1.07)
0.15
ED or urgent
care visit
199 257
0.81
(0.63 - 1.04)
0.09
Unscheduled
office visit
1202 1345
0.85
(0.74 - 0.98)
0.02
Adapted from Table 2 from NEJM 2011; 365:689
20. Statistical Approach to Compare 2
Groups
Calculate:
1. Main effect
2. Variance in main effect
State a null hypothesis
(the main effect is 0)
Calculate the test statistic
to determine p value
Calculate the 95%
confidence interval around
the main effect
New Drug Placebo
22. Statistical Tests
Mathematical formulas that produce test
statistics to assess the likelihood that
chance (or sampling error) accounts for
the results observed in the study
Many different tests. Choice depends on
several factors:
Type of data (continuous, dichotomous, etc)
Distribution of data (normally distributed or not)
Study design (# of groups, etc)
25. P-value
Probability that the results seen (or one more
extreme) could have occurred by chance
alone
○ Assuming that there is in fact no difference
between groups (null hypothesis)
Cannot tell you if there is bias in a study
Does not indicate clinical significance
26. To learn more watch my other
videos
NNT: http://bit.ly/1F4xONy
RRR: http://bit.ly/1Fyef3F
32. Establish incidence
(risk) directly
Multiple outcomes
Study of rare exposures
Strengths Weaknesses
Not good for rare
diseases
Not good for diseases
that take a long time to
develop
Can’t study multiple
exposures
Cohort: Strengths &
Weaknesses
33. The incidence of pulmonary embolism in the COPD
cohort was 1.37 per 10,000 persons/year and in the
non-COPD cohort was 0.35 per 10,000
persons/year.
Multiple ways to express risk
Incidence
Risk difference (attributable risk)
Relative risk (risk ratio)
Interpreting RR
RR = 1 (no association)
RR > 1 (increased risk of disease)
RR < 1 (decreased risk of disease)
http://bit.ly/1dtFFhV
36. Good for diseases with
long latency
Good for rare diseases
Can determine multiple
exposures
Faster results
Strengths Weaknesses
Can’t establish estimate
of risk directly nor
determine prevalence
Can only study one
disease
More prone to bias
Case-Control: Strengths &
Weaknesses
37. Low-dose glucocorticoid use (prednisolone daily dose equivalent
5 mg) carried a twofold increased risk of PE (OR, 1.8; 95% CI,
1.3-2.4), whereas a 10-fold increased risk was observed for the
highest dose of glucocorticoids (prednisolone 30 mg) (OR, 9.6;
95% CI, 4.3-20.5). The authors are incorrect in the statements of
risk. Do you know why?
Can only determine relative frequency of
exposure among cases and controls
Odds ratio
Interpreting OR
OR = 1 (no difference of exposure)
OR > 1 (frequency of exposure higher among cases)
OR < 1 (frequency of exposure lower among cases)
http://bit.ly/1HHm2Nd
38.
39. Screening
Prevalence vs incidence screens
Outcomes of screening studies
Biases
Lead time
Length time
Overdiagnosis
40.
41. Identification of disease or a risk factor in
asymptomatic individuals
Screening
Biologic Onset Outcomes
Clinical
diagnosis
Screen
detection
42. Fundamental Principles of
Screening-1
3 prerequisites:
▪ Disease must have a great enough burden of
suffering
▪ Screening test can identify disease earlier than
usual
▪ Earlier therapy leads to better outcomes
43. Fundamental Principles of
Screening-2
Target disorders are relatively rare (low
prevalence)
Must screen large numbers of people
Most positive tests are false positives
Risks of screening tend to be rare but apply
to all
Benefits accrue only to a few
44. Disease Prevalence is Low
LOW low predictive value
Sensitivity=95%
Specificity=95%
LR=19
Prevalence Predictive value
10% 67%
1% 16%
0.1% 1.8%
Watch Predictive Value Estimates From Studies Can Be Misleading
http://youtu.be/3zq82uiGS3o
45. When choosing a test for a screening
program you want the test to be….?
1. Highly sensitive
2. Highly specific
46. Do you find more cases of disease
on the first round of screening or
subsequent rounds?
Dx
Dx
Dx
Dx
Dx
Dx
Dx
Dx
Dx
Dx
Dx
Dx
1 2 3Round of screening
Number of cases newly
detected
5 3 2
47. What is the appropriate
outcome of a screening study?
A. Survival?
B. Mortality?
C. Disease detected?
48. Solving lead time bias problem: compare age-specific mortality between
screened and unscreened. Not survival! Count from date of randomization
Adapted from Clinical Epidemiology The Essentials 3rd edition
Dx †
Dx †
Unscreened
Screened but
early Rx
ineffective
Lead Time Bias
50. Compare outcomes via RCT with a
control group and a group offered
screening
Count all outcomes regardless of
method of detection
Avoiding Length Time Bias
51. Is PSA screening causing prostate
cancer ???
From cancer.org
PSA approved