Module 3 Flashcards
Rothman Module 3, Lecture 3
What is the Likert Scale?
In its final form, the Likert scale is a five (or seven) point scale that is used to allow an individual to express how much they agree or disagree with a particular statement.
It is controversial in its unobjective and forced responses.
What is nominal data?
categorical / qualitative data; categories as values which differ in quality
What is ordinal data?
Nominal data that are ordered in some way (good, better, best / small, medium, large / 1,2,3)
What is interval data?
There is a meaningful and definable distance between the categories of measurement. There is no fixed relationship to zero.
(e.g. temperature - 100 is 10 degrees more than 90, but 100 is not twice as hot as 50; 0 also does not represent the “absence” of temperature)
What is ratio data?
Has all the properties of interval data, but there is a meaningful relationship to zero
(e.g. height, weight, enzyme activity, bacterial counts…. someone who weighs 200 pounds weights twice as much as someone who weighs 100 pounds).
What is a ratio?
The size of something compared to the size of something else; a/b
What is a rate?
(a+b) / time ; the change in a subset compared to the change in the set per unit time
What is the most commonly used rate in epidemiology?
incidence - events (a) per person (b) per time (t) = a/b/t or a/bt
e.g. 10 people are observed for 10 years (100 person years).. 6 get heart attacks. The incidence of heart attacks in this group is 6 per person years.
What is a proportion?
the size of a part relative to the whole (a/a+b)
What is the cumulative incidence / proportion?
the number who moved into the numerator (na) divided by the total number of people at the beginning (b) minus the ones who left the denominator; na/(b-na)
What are the numerator and denominator in relation to incidence?
Events in the numerator are things (infections) that happen to people in the denominator. That means when an event occurs, people are moved from denominator to numerator. Both will change - the numerator gets bigger and the denominator smaller.
What is the difference between incidence and prevalence?
Incidence is answering the question: “how fast is something occurring?”
Prevalence is concerned with the question: “how much is there at some point in time?”
What is point / period prevalence?
numbers of cases per population at some instant. This is usually impossible to measure, so the term “Period Prevalence” is used.
What is the relationship of prevalence, incidence, and duration?
Prevalence = Incidence x Duration
How do we determine the difference between groups in research?
the size of the difference (count)
the dispersion of the data (a ratio)
the number of observations used to determine the point data / sample size (count)
The larger the sample, the more likely you are coming closer to a true number
Who first referred to the “Distribution around the mean”?
Carl Friedrich Gauss
What is normal distribution / distribution around the mean?
Normal distribution, also known as the Gaussian distribution, is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean. In graphical form, the normal distribution appears as a “bell curve”
What is a Z score?
Z-score is a statistical measurement that describes a value’s relationship to the mean of a group of values.
The higher (or lower) a z-score is, the further away from the mean the point is.
What is a standard deviation?
The standard deviation is the average amount of variability in your dataset. It tells you, on average, how far each value lies from the mean.
What is a t test?
A t test is a statistical test that is used to compare the means of two groups. It is often used in hypothesis testing to determine whether a process or treatment actually has an effect on the population of interest, or whether two groups are different from one another.
What is the ultimate goal of validating research outcomes?
To achieve generalizability
What is an odds ratio?
It is a measure of association between an exposure and an outcome
As an example, if the odds ratio is 1.5, the odds of disease after being exposed are 1.5 times greater than the odds of disease if you were not exposed another way to think of it is that there is a 50% increase in the odds of disease if you are exposed.
Here it is in plain language. An OR of 1.2 means there is a 20% increase in the odds of an outcome with a given exposure. An OR of 2 means there is a 100% increase in the odds of an outcome with a given exposure. Or this could be stated that there is a doubling of the odds of the outcome.
What is accuracy versus precision?
Precision and accuracy are two ways that scientists think about error. Accuracy refers to how close a measurement is to the true or accepted value. Precision refers to how close measurements of the same item are to each other.
What is validity in research?
how well the results among the study participants represent true findings among similar individuals outside the study.
The term validity refers to the correctness of the conclusions that are drawn from the results. In other words, how accurate are the results? Do the results actually measure what was intended to be measured? It is important to assess if a study was conducted so that each of its elements is defensible, and their interaction produced a coherent “story” with regard to the findings.
Threats to validity include: (1) measurement error—the exposure and the outcome were measured correctly; (2) misclassification—either persons or exposures were placed in the wrong categories; (3) bias—non-systematic mistakes (different for cases and control in a study) that distort the results; (4) incorrect or inappropriate analytic procedures.
What is reliability in research?
Reliability refers to how consistently a method measures something. If the same result can be consistently achieved by using the same methods under the same circumstances, the measurement is considered reliable.
Test & retest in different circumstances
What is falsifiability in research?
Falsifiability is a cornerstone of the scientific method. It refers to the idea that, to be a valid scientific hypothesis, it must be possible to disprove it.
What is generalizability in research?
Generalizability refers to whether or not the research findings and conclusions that result from the study are applicable to other populations or, more broadly, to everyone.
The Framingham Heart Study (which utilized only white men) is a great example of what NOT to do
Are the following examples a rate, ratio, count, or proportion?
- Components of a recipe for chocolate cake
- The prevalence of tuberculosis
- The speed of light
- Infant mortality (per live births)
- Ears of corn produced per acre cultivated
- Cases of flu seen in a clinic per month
- Count
- Proportion
- Rate
- Ratio
- Rate
- Proportion
What is the epidemiologic triangle?
Agent, host, and environment
What are different types of infectious agents?
Biological Microorganisms, Pathogens, such as :
Bacteria, viruses, rickettsia, fungi and yeast, Helminthes, Protozoans, Prions
Chemical:
poison, alcohol, smoke
Physical:
trauma, radiation, fire
Nutrition:
lack, excess
What are environmental factors associated with increased risk of disease?
temperature
air pollution
crowding
neighborhood
sanitation
healthcare access
vector control (of certain animals e.g. birds or mosquitos)
What are host characteristics associated with increased risk of disease?
Age
sex
cultural practices
Socio economic status
What is infectivity?
ability to establish infection in an exposed person
What is pathogenicity?
ability to cause disease in infected person
What is virulence?
how sick an infected person gets
What is a host and its risk factors?
An organism (usually human or animal) that harbors a disease
Risk factors: exposure, susceptibility, response
What is an environment in epidemiology?
surroundings / conditions external to the human or animal (host) that cause or allow disease transmission
What are reservoirs?
The habitat (living or nonliving) on which an infectious agent lives, grows, and multiplies and is dependent on for its survival in nature
Can be environment or humans / animals (they can be both hosts and environments)
What are the types of reservoirs?
Symptomatic cases (people with apparent signs of infection)
Carriers / asymptomatic cases
Zoonoses (animal carriers, often with complex life cycles, multiple hosts, and insect vectors)
Environment (food, water, soil, air, and other inert substances)
How many diseases are zoonotic according to the CDC?
around 60% of all diseases
What are portals of infection entry / exit in the human body?
respiratory tract
conjunctiva (eyes)
uro-genital tract
gastrointestinal tract
skin
placenta
most agents have a preferred portal; blocking that portal can prevent infection
What are modes of transmission?
Any mechanism by which an infectious agent is propagated (spread) - bridging the gap between portals; Person to person contact
Indirect transmission (pathogens or agents are transferred onto an intermediate source - vehicle-borne (objects), airborne, vector-born (animals)
What are examples of types of transmitted diseases?
Direct contact: ebola, impetigo, warts
Fecal - oral: Cholera, rotavirus, salmonella
Sexual: HPV, herpes, syphilis, chlamydia
Indirect - vector borne (Malaria, West Nile, Lyme)
Vehicle Borne (cryptosporidiosis), Campylobacteriosis
Airborne (anthrax, measles, influenza)
What is susceptibility defined?
at risk of contracting a disease
What is immunity defined?
the factors that alter the likelihood of infection and disease in the host when the agent is encountered
-innate / nonspecific immunity (present at birth, body’s first line of defense)
-acquired immunity (learned, body recognizes non-self antigens and develops memory to fight it)
What are the types of acquired immunity?
Active - from artificial or natural exposure (vaccines)
Passive - from maternal sources, therapeutic doses or immune serums and antitoxins
What is immunogenicity?
a person’s ability to produce an immune response after vaccination or infection
What is herd immunity?
the proportion of individuals in the population who are resistant to a particular disease
(Once a high percentage is achieved, disease cannot spread)
What is R0 (R naught?)
the expected number of secondary cases produced by a single (typical) infection in a completely susceptible population
If <1, outbreak will die out
If >1, epidemic will grow
What are the links in the chain of infection?
pathogen / infectious agent > reservoir > mode of transmission > host
What is the herd immunity threshold?
The average number of additional cases that occur from a single case in a susceptible population with no interventions (e.g. no vaccinations)
Describe the ecosocial framework:
What is a case, defined?
A person who has been diagnosed as having a disease, disorder, injury, or condition
What is the primary case?
first disease case in a population
What is the index case?
first case brought to the attention of the epidemiologist
(is not always primary)
What are secondary cases?
persons who become infected / ill after a disease has been introduced to a population via contact with the primary case
What are suspected and confirmed cases?
Suspected: person who has all signs and symptoms of a disease yet is not diagnosed
Confirmed: person confirmed with diagnosis as more info becomes available to physician (e.g. updated diagnosis info / disease definition, lab results)
What is the triangle of modern epidemiology?
behavior, lifestyle, and chronic disease issues
What is etiology?
the cause, set of causes, or manner of causation of a disease or condition.
typically both environmental and genetic, but sometimes only 1 is needed
Need motivation to change prior to fear and pain
Describe the chronic disease epidemiological triangle
What is the natural history of disease?
this refers to the progression of a disease in an individual over time
Describe the natural history of disease schematic
What are types of non-clinical (in-apparent) disease?
Preclinical disease (not yet clinical but destined to become so)
Subclinical disease (not clinically apparent and not destined to become so; usually determined via antibodies or cultures)
Persistent / Chronic Disease (inability to rid infection; may persist or disappear / reappear continually)
Latent disease (infection with no active multiplication of the agent)
What are the three tiers of prevention?
Primary: avert disease before it develops (e.g. vaccinating children)
Secondary: early detection of disease in attempts to prevent or cure it (e.g. annual mammograms)
Tertiary: stop or limit spread of disease already present (prevent disability)
What is endemic?
Habitual presence of a disease within a given demographic area
What is epidemic?
Occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy and derived from a common or propagated source
What is pandemic?
worldwide epidemic
What are the main reasons epidemics occur?
Susceptible people travel to an endemic area
They engage in new / unusual social, behavioral, or cultural practices
Host susceptibility and response typically adjusted by immuno-suppression or malnutrition or other diseases
Why do epidemics end?
no more susceptible individuals / susceptibility decreases
no more exposure to the source / contamination
pathogen becomes less able to produce disease (less pathogenic)
What are common epidemic interventions?
Control the source of the pathogen (remove source or exposure opportunities, sterilize pathogen, treat or quarantine)
Control or modify host response to exposure (modify behavior, use barriers)
Interrupt the transmission (vector control, personal hygiene)
What are types of disease outbreaks?
Common vehicle exposure:
single exposure (point source, unlikely to create secondary cases)
multiple exposure (continuing common source)
Propagated (person to person transmission)
How do we achieve herd immunity?
once the probability of an infected person encountering every other person in the population is the same (random mixing)
What are qualifications of herd immunity?
- Disease restricted to a single host species
- Relatively direct transmission from one host to another
- Infections must induct solid immunity
- Outbreaks only occur in randomly mixing populations
What is an incubation period (defined)?
Interval from receipt of infection to the time of onset of clinical illness
What is an epidemic curve?
Plot of the number of cases against the time of onset of a disease
(In a single exposure, this will show distribution of incubation periods)
What are some reasons for epidemiologic transition?
Medical technology
Improved standard of living
Birth control
Improved nutrition
Sanitation and vector control
Improvements in lifestyle
According to the CDC, what are the top 10 public health achievements?
- Vaccination
- Motor vehicle safety
- Safer workplaces
- Control of infectious diseases
- Decline in deaths from heart disease / stroke
- Safer and healthier foods
- Healthier moms and babies
- Family planning
- Fluoridation of drinking water
- recognition of tobacco as a health hazard
Describe disease prevention efforts
Describe the Iceberg of infectious disease
