Introduction to survival analysis Providing intuition of hazard function, survival function, cumulative failure function. Life table, KM and log-rank test
Introduction to survival analysis Providing intuition of hazard function, survival function, cumulative failure function. Life table, KM and log-rank test
Cohort, case control & survival studies-2014Ramnath Takiar
The presentation discusses about Cohort, Case-control and Survival studies. The concept of Cohort and Case-control studies is explained with the help of diagrams as perceived by me. Some discussion is also there about survival and relative survival. Appropriate data is also provided to explain about survival and relative survival.
Excelsior College PBH 321 Page 1 BIAS IN EPIDE.docxgitagrimston
Excelsior College PBH 321
Page 1
BIAS IN EPIDE MIOLO GY
THE MEANING AND CONTEXT OF BIAS
We briefly touched upon bias earlier in the course. The word bias probably has an intuitive meaning to you,
and recall the definition from Module 3:
“Deviation of results or inferences from the truth, or processes leading to such deviation. Any trend in the
collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are
systematically different from the truth.” (J.M. Last, A Dictionary of Epidemiology, 4th ed.)
Bias is a systematic error that results in an incorrect (invalid) estimate of the measure of association. Bias can
therefore create the appearance of an association when there really is none (bias away from the null), or mask
an association when there really is one (bias towards the null). Bias can arise in all study types: experimental,
cohort, and case-control designs. It is primarily introduced by the investigator or study participants in the
design and conduction of a study, and once it occurs, cannot be removed – but it can be evaluated during the
analysis phase of a study. Bias is a direct threat to the validity of any epidemiologic study, and influences
whether we can believe the observed association is a true association.
DIRECTION OF BIAS
We can describe the impact of bias on the measure of association in a few different ways. Remember, the null
value is 1.0; the value that means there is no observed association between exposure and disease. If the true
association is protective (less than 1.0), bias towards the null will make it seem less protective as the measure
of association gets closer to the null value.
• Positive bias: the observed value is higher than the true value
• Negative bias: the observed value is lower than the true value
• Bias towards the null: the observed value is closer to 1.0 than the true value.
• Bias away from the null: the observed value is farther away from 1.0 than the true value.
Bias towards null
Bias away from null
Bias away from null
Bias towards null
Protective effects Harmful effects
1.0
(no association)
Bias towards null
Bias away from null
Bias away from null
Bias towards null
Protective effects Harmful effects
1.0
(no association)
Excelsior College PBH 321
Page 2
TYPES OF BIAS
Two main types of bias are selection and information (observation) bias. You had an introduction to these
biases in Module 4.
1. Selection Bias
Selection bias is error that occurs if selection of subjects into a study is related to both exposure and disease.
As a result, the measure of association differs from what would have been obtained if we could examine the
entire population targeted for study. Selection bias is most likely to occur in case-control or retrospective
cohort studies because exposure and outcome have occurred at time of study selection, and may influence
the willing ...
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
2. Learning Objectives
When you have completed this session you will be
able to:
Describe the characteristics of a cohort study
List the types of bias most likely to affect a cohort
study
List the conditions under which a cohort study is an
appropriate choice to address a research question
Describe the advantages and disadvantages of
cohort study
4. But sometimes also: Why?
What are the risk factors for neonatal
tetanus?
What factors are associated with increased
mortality for persons with measles?
Does smoking cause lung cancer?
Analytical epidemiology
5. Analytic Studies
To test whether certain factors are “associated”
Association is a statistical concept
To look at association we need to move away from
description of a factor in one group
We need a “comparison group”
Is cancer more common in those exposed to uranium
compared to those who have never being exposed ?
Is uranium associated with cancer ?
Is this association statistically significant ?
Could it have occurred by chance ?
9. What is a cohort?
Cohort: Latin word for 1 of the 10 divisions
of a Roman legion
A group of individuals
sharing same experience
Followed-up for a specified period of time
Examples
birth cohort
Workers at a chemical plant
KIU first cohort
10. Design of a Cohort Study
Individuals
“choose” their
exposure status
11. Sub-classifications of Cohort Studies
Time perspective
Prospective
Retrospective
Population dynamics
Closed population
Open population
12. Terminology: Retrospective or
Prospective?
Suggest use the terms “retrospective” or
“prospective” to refer to the timing of events
in relation to initiation of study.
(Hennekens and Buring, 1987)
Retrospective cohort study: exposure and
disease have occurred prior to start of study
Prospective cohort study: disease has not
occurred prior to start of study
14. Prospective Cohort Study
Chernobyl, Industrial accidents, Flood victims
+
-
+ -
ill
exp
+
-
exp
Disease
occurrence
Study startsExposure
occurrence
Prospective assessment
of disease
Selection based
on exposure
15. Steps in a prospective cohort study
Define the population at risk (=cohort)
Determine exposure to a factor of interest of all
subjects in the cohort
Follow exposed and non-exposed forward in time
to ascertain whether they develop the outcome of
interest
Compare the outcomes in the exposed and the
unexposed group with each other
16. Foodborne outbreaks, closed environment outbreaks (school, prisons,
…)
Retrospective Cohort Study
Study
takes place
Disease
occurrence
Exposure
occurrence
Retrospective assessment
of exposure and disease
Selection based
on population
+
-
+ -
ill
exp
17. Retrospective cohort studies
• Well defined population
• Exposed and unexposed can be identified
• Outcome (ill or not ill) can be ascertained
Opportunity to go back in time,
categorise people according to their exposure
and then determine their outcome
For example, weddings, parties, hotels, occupational
exposures, etc.
18. Closed and Open Populations
Closed population
adds no new members over time
loses members only to death
Open population
may gain members over time (immigration or
birth)
may lose members who are still alive through
emigration
19. Issues in Design of Cohort Studies
Sources of Data
Exposure Information
Pre-existing records
Availability for much of cohort
Inexpensive
Objective, bias-free categorisation of exposure status
But – insufficient detail and no information on potential
confounders
Information from study subjects
Information on data not routinely collected
Questionnaires/interviews
Potential bias
Ascertainment of exposure must be comparable for all
20. Issues in Design of Cohort Studies
Sources of Data
Outcome Information
Obtain complete, comparable, unbiased information
Death certificates (potential bias when cause-
specific mortality)
Medical records, Medical Aid schemes, etc.
From study subjects
Periodic direct medical examinations
Apply equally to exposed and non-exposed
21. Biases in Cohort studies
1. Loss to follow up
Failure to ascertain outcome data is the major
source of potential bias
Length of follow-up period is related to latency
period of disease
The longer the follow-up period the more difficult
to ensure complete data
If lost to follow-up is large (eg, 30-40%) ?
Validity ?
Loss to follow-up may be differential
22. 2. Participation bias
Agreeing participants may differ from non-
participants
This affect external validity more then internal
3. Misclassification bias
Misclassification due to exposure status is
common
Can be random (equally for exposed and
unexposed) or non-random
23. 4. Ascertainment bias
Biases in ascertaining the outcome.
Outcomes should be ascertained equally by
exposure status
24. Distribution of illness according to
exposure in a cohort study
Exposed
Not exposed
ILL NOT ILL
a b
c d
a+b
c+d
Incidence
a+b
c+d
a
c
Relative risk = Incidence exposed / Incidence not exposed
25. Cohort study about bottled water as
risk factor for illness
Drink bottled
water
40
30
30
Risk
30
40
Relative Risk (RR) = 30 /
405 /
30
=
4.4
ILL NOT ILL
10
255
Do not drink
bottled water
5
30
26. Interpretation of Relative Risk
The risk of illness among those who drink
bottled water is 4.4 times higher than among
those who do not drink bottled water.
27. Advantages of cohort studies
Directly measure risk or rate
Measures of effect have clear meaning and are
easily understandable
Temporal relationship between exposure &
disease can be established
Prospective cohort studies less susceptible to
selection bias because outcome not known
Well suited to rare exposures
Several outcomes can be examined in one study
28. Disadvantages of cohort studies
Large sample size
Latency period
Loss to follow up
Exposure can change over time
Multiple exposures = difficult
Cost
Time consuming
29. Recap
Now that you have completed this session you should
be able to:
Describe the characteristics of a cohort study
List the types of bias most likely to affect a cohort
study
List the conditions under which a cohort study is an
appropriate choice to address a research question
Describe the advantages and disadvantages of
cohort study versus a case-control study
Editor's Notes
Please do not change the learning objectives without notifying the team.
Move any learning objectives that you don’t expect to cover in class to the “What’s next” slide at the end of the presentation.
For ascertainment can use physical examination, proxy measures ( job title, distance from source) direct measurement (water, air pollution) but that is a problem if exposure occurred before study began. Consider need for baseline assessment and periodic reassessment as it may change over time.
Discuss problems with lost to follow-up and how those lost may differ in important ways from those who are not lost.
Please do not change the learning objectives without notifying the team.
Move any learning objectives that you don’t expect to cover in class to the “What’s next” slide at the end of the presentation.
