What is Cohort?
Indication and Elements of Cohort Study.
What is Relative risk and Attributable risk, and its interpretation?
Advantages & disadvantages of Cohort study.
Difference between Case control & Cohort study.
In this presentation i tried to explain in detail about cohort studies, their types, how to conduct them, their outcomes, and how to calculate sample size of these studies.
What is Cohort?
Indication and Elements of Cohort Study.
What is Relative risk and Attributable risk, and its interpretation?
Advantages & disadvantages of Cohort study.
Difference between Case control & Cohort study.
In this presentation i tried to explain in detail about cohort studies, their types, how to conduct them, their outcomes, and how to calculate sample size of these studies.
Systematic (non-random) error that results in an incorrect estimate of the association between exposure and risk of disease.
Can occur in all stages of a study
Not affected by study sample size
Difficult to adjust for afterwards, but can be reduced by adequate study design.
•Can never be totally avoided, but we must be aware of it and interpret our results accordingly
Error/Bais in Rsearch Methodology and pharmaceutical statisticsakashpharma19
Error/Bais in Rsearch Methodology and Pharmaceutical Statistics .
A biased estimate is
one which, on the average, does not equal the population parameter.
EpidemiologyUnit 3Bias, Error, Confounding and Effect Modification4hrs
Radha Maharjan
MN(WHD)
Contents
3.1 Bias and Error in Epidemiology
3.1.1 Bias (Researcher and Respondent)
Recall Bias
Information Bias ( sponsor bias, social desirability bias, acquiescence Bias)
Selection Bias
Confirmation Bias
The halo effect.
Contents
3.1.2 Error
Systematic Error
Random Error
Confounding & Effect Modification
Definition of Error
A measure of the estimated difference between the observed or calculated value of a quantity and its true value.
Random error or Chance
It is the by-chance error
It makes observed value different from the true value
May occur through sampling variability or random fluctuation of the event of interest due to
biological variability, sampling error and measurement error (not due to machine)
lack of precision in the measurement of an association
Biological variability:
The natural variability in a lab parameter due to physiologic differences among subjects and within the same subject over time.
Differences between subjects due to differences in diet, genetics or immune status.
Sampling error:
Sampling error is a statistical error that occurs when an analyst does not select a sample that represents the entire population of data.
Measurement error:
Measurement Error (also called Observational Error) is the difference between a measured quantity and its true value.
Random error or Chance
Random error can never be completely eliminated since we can study only a sample of the population.
Random error can be reduced by
careful measurement of exposure and outcome
Proper selection of study
Taking larger sample- increase the size of the study.
Systematic error or Bias
Systematic error (or bias) occurs in epidemiology when results differ in a systematic manner from the true values.
Bias is any difference between the true value and observed value due to all causes other than random fluctuation and sampling variability.
This type of error is generally more insidious and hard to detect.
Systematic error or Bias
For example over-estimate of blood sugar of every subject by 0.05 mmol/l resulted from using inaccurate analyser.
The possible sources of systematic error are many and varied but the important biases are selection bias, measurement bias, confounding, information bias, recall (respondent) bias, etc..
Sources of error in epidemiological study
Common sources of error are
selection bias
absence or inadequacy of controls
unwarranted conclusions
improper interpretation of associations
mixing of non-comparable records
errors of measurement (intra-observer variation, inter-observer variation), etc.
The error can be minimised through
study design (by randomisation, restriction & matching) and
during analysis of the results (by stratification and statistical modelling) ..
Selection bias
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Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
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The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
ARTIFICIAL INTELLIGENCE IN HEALTHCARE.pdfAnujkumaranit
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Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
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Bias and Confounding
1. Bias and Confounding
Dr. Faiza Abou El-Soud
Prof. of Community Health Nursing
Menoufiya University -Egypt
2. Learning Objectives
§Define bias, confounder and related terms
§ Discuss types of bias in the epidemiological
study
§ Elaborate methods of handling confounder
3. Definition of Bias
• “Any systemic error (design, data
collection, analysis or reporting of a study)
in epidemiological study that results in
incorrect the estimation of the association
between exposure and outcome”
• “Deviation of results or inferences from
the truth”
4. Properties
of
Measurement
• alidity (Accuracy): Validity is how much a
test measures what it is supposed to
measure.
• eliability (precision): Reliability is the
consistency of test results
6. I. Selection Bias
• Occurs when the two groups being compared
differ systematically
• That is, there are differences in the characteristics
between those who are selected for a study and
those who are not selected
• Most common type of bias in health research
• Seen in observational and analytical studies
7. I. Sources of Selection Bias
1. Volunteer Bias
• Occurs when the participants select themselves for a study,
either because they are unwell or because they are
particularly worried about an exposure.
• , that people who respond to an invitation to
participate in a study on the effects of smoking in their
smoking habits non responders, the latter are usually
heavier smoker.
8. 2.Non-response Bias
• Occurs because individuals who do not respond to a call or
mailed questionnaire to participate in research studies are
generally from those who do respond.
• , smokers are less likely to return questionnaire
than are non-smokers
9. 3. Exclusion Bias
• Occurs when in certain circumstances epidemiologic studies
exclude participants to prevent confounding.
• , when exclusion criteria is different for cases and
control, or exposed and non-exposed
11. Information Bias
• Occurs as a result of misclassification of
or status.
• For example,
• The figure below shows a two-by-two
contingency table in which apparent
that subjects are in the cell
of the contingency table, but there are
who have been misclassified and
are in an cell.
12. 1. Interviewer Bias (Abstract bias)
An interviewer’s knowledge may influence and the
, which may influence responses.
If an interviewer has a about the hypothesis being tested,
he or she might consciously or unconsciously interview case subjects differently
than control subjects.
If a reviewer believes that the research hypothesis was , the medical
record of a case subject might be looking at more thoroughly to find evidence of
exposure.
interviewers who believe that there is an association might
question case subjects more strictly in order to encourage cases to a past
exposure, while not prompting controls in the same way.
13. 2. Recall Bias
• , the subjects who are with a particular outcome or exposure
may more clearly.
, in case-control studies, this bias occurs when certain
information recalled by the (cases) compared with (controls).
Therefore, this missed of information, such as a potentially relevant
exposure, may be recalled by the (case) but forgotten by the (control).
• For example, congenital disorder remembers
every events clearly during pregnancy
14. 3.Reporting Bias
• Occurs when the participants can collaborate with researchers
and give answers in the directions they perceive are of
interest.
For example,the participant (either among the cases or among
the controls) may be to report an
exposure/event he is of because of
Therefore, this report bias
may affect the result.
15. 4.Surveillance Bias
• It is called or
• Occurs when the study group with known exposure or outcome may be
followed closely or longer the comparison group.
• It occurs when subjects in one exposure group are more likely to have
the study ourcome detected because they receive increased surveillance,
screening or testing as a result of having some other medical condition
for which they are being followed.
• obese patients are more likely to undergo medical
examinations, blood tests, and imaging studies than non-obese people.
If obese subjects were being compared to non-obese subjects
The early cancers reseraches would be more likely to be found in the
obese group, an of the .
16. 5. Withdrawal Bias ( )
• is other sources of bias that may found
some participants those are lost to follow up or who
withdraw from study may be different from those who are
followed in the study.
17. • This Hawthorne effect is other sources of bias that found
among some people act differently if they know they are
being watched.
• For example, One study was performed at a factory to
if change in lighting would affect
productivity.
• Therefore, productivity did increase but only because of
increased attention due to the study, as soon as study had
ended productivity decreased again.
18. Confounding
When another exposure exists in the study population (besides
the one being studied) and is associated both with disease and
the exposure being studied.
Confounder must be…….
1. Risk factor for the disease independently
2. Associated with exposure under study
3. It is not casual pathway between exposure and disease
For example,
age , sex ,living condition
21. Control of Confounding
At design stage:
• -Restriction
• -Matching
• -Randomisation
At analysis stage
• -Stratification
• -Multivariate analysis
22. Restriction
• Subject chosen for study are restricted to only those
possessing a narrow of characteristics , to equalize
important extraneous factors.
For example,
• Restrict study to women having
23. Matching
• For each patient in study group there is one or more patients
in comparison group with same characteristics, for the
factor of interest.
For example,
• Matching done for age ,sex ,race etc.
25. • The process of separating a sample into several sub-samples
according to specified criteria such as age group ,
socioeconomic status etc.
Stratification
26. The statistical analysis of data collected on more than one
variable.
For example,
People age ,weight, body fats . Skull length, width and cranial
capacity