EXAM 2 Material

Question 1

Define the term cause

Answer 1

An event, condition or characteristic without which the disease would not have occured.

Question 2

Distinguish between the deterministic and probabilistic models of causality and provide examples of each type.

Answer 2

Deterministic: claims that in order for a disease to occur a cause and effect relationship is necessary; types: necessary and sufficient causes and sufficient-component causes.
Probabilistic: involves probabilistic model, aka: stochastic model→ stochastic process: incorporates some element of randomness; a cause is associated with the increased probability that an effect will happen.

Question 3

Distinguish between a cause that is sufficient but not necessary and one that is necessary but not sufficient. Be sure to give examples.

Answer 3

Sufficient but not necessary: factor (X) may or may not be present when disease (Y) occurs. X is one of the casuses of Y; but there are others. Ex: HCl is sufficient to cause a skin burn, however HCl is not necessary to cause a skin burn.
Necessary but not sufficient: Factor(X) must be represented for disease ( Y) to occur, but factor (X) may be present without disease (Y) occurring. X is necessary to cause Y, but X by itself does not cause Y. Ex: Exposure to HIV is necessary to cause AIDS to develop, but not all individuals exposed to HIV will develop AIDS. You have to have the virus to get the disease, but you do not have to be exposed to the disease to get the virus. ** Most infectious diseases are like this**.

Question 4

Describe the sufficient-component cause model, and using your own ideas, give an example.

Answer 4

Causal pie model, constituted from a group of component causes, which can be diagrammed as a pie.
Necessary cause : this is a common piece of the pie; A factor(X) whose presence is required for the occurrence of the effect (Y). The remaining components are not necessary.
Component cause: a slice of the pie; the necessary cause (slice A) is always accompanied by an additional set of component causes ( the other slices).

Question 5

Describe the types of associations

Answer 5

Association: variables that are associated with one another can be positively or negatively related.
Positive Associations: if the value of one variable increases, the value of the other variable increases as well
Negative association: If the value of one variable increases, the value of the other variable decreases.
Types: Stat association ?: Y/N → if no, X is unrelated to Y, if yes, X is related to Y,
what kind of association : Noncausal → X does not cause Y, Causal → X causes Y

Question 6

Describe the types of associations (noncausal, causal, direct, indirect) that are possible among exposures and health outcomes.

Answer 6

Types: Stat association ?: Y/N → if no, X is unrelated to Y, if yes, X is related to Y,
what kind of association : Noncausal → X does not cause Y, Causal → X causes Y
Indirect association →
Direct association → a graphical approach depicting causal relationships : * Nomenclature: Arc→ Line/ Arrow connecting two variables, single–headed arrows represent DIRECT links from cause to effect. Node → points on the graph (variables). Path → unbroken route traded out along or against arrows/ lines connecting nodes.
Direct (causal) path : a sequence of single- headed arrows,
Back door path: non-causal pathway between variables.

Question 7

What is the criteria for causality

Answer 7

one of the central concerns of epidemiology is to be able to assert that a causal association exists between an exposure factor and disease in the host. ex : is there a causal relationship between smoking and lung cancer?

Question 8

Identify Randomized clinical trial by its description

Answer 8

experimental manipulation, randomization : used to test the efficacy of preventive or therapeutic measurements, focus on the individual, prospective. AKA; Randomized clinical trial. Designs of Clinical trials: investigator manipulates study factor, investigator randomly assigns subjects to the treatment, permits the calculation of incidence rates. The outcome of the interest (clinical end point) is measured in the intervention and control arms of the trial to evaluate efficacy : may include rated of disease, death, or recovery, these must be measured in a comparable manner, once a clinical trial shows early evidence of efficacy or insufficient evidence to justify continuation, the trial must stopSingle and double blind. There are 4 phases
Types : Prophylactic Trials: prevent disease, eval the effectiveness of a substance that is used to prevent disease, Therapeutic Trials : improve health, involve the study of curative drugs or a new surgical procedure to improve the patients health.

Question 9

Identify a Community Trial by its description

Answer 9

An experiment in which the unit of allocation to receive a preventative, therapeutic, or social intervention is an entire community or political subdivision. ( school, county, school district), help determine the potential benefit of new policies and programs. Steps; determine eligible communities and their willingness to participate, 2) collect baseline measures of the problem to be addressed in the intervention and control communities, 3) use a variety of measures eg : disease rates, knowledge, attitudes, and practices, 4) communities are randomized and followed over time. 5) outcomes of interest are measured.

Question 10

What are the advantages of Community trials

Answer 10

represent the only way to estimate directly the impact of change in behavior or modifiable exposure on the incidence of disease. Disadvantages: inferior to clinical trials w/ respect to ability to control entrance into study, delivery of the intervention, and monitoring of outcomes. Fewer study units are capable of being randomized, which affects comparability, affected by population dynamics, secular trends, and non intervention influences.

Question 11

Describe a prophylactic and give examples.

Answer 11

Prophylactic Trials: prevent disease, eval the effectiveness of a substance that is used to prevent disease, Ex: Steps: 1) randomly assign treatment 50 w/ treatment, 50 w/o treatment., 2) Follow up for outcome (disease) ex: 50 w/ treatment : 2 incidence , 50 w/o treatment : 6 incidence Ex: Vaccine is a preparation of killed or weakened microorganisms (bacteria, virus) that is administered to produce antibodies against a particular disease.

Question 12

Describe therapeutic trials and give examples

Answer 12

Therapeutic Trials : improve health, involve the study of curative drugs or a new surgical procedure to improve the patients health. Steps: 1) randomly assign treatment 10 w/o treatment, 10 treatment., 2) follow up for outcome (death) → 10 treated : 3 dead, 10 w/o treatment = 5 dead (control)

Question 13

What is the purpose of blind masking in an experimental study

Answer 13

to maintain the integrity of a study and reduce the potential for bias, the investigator may utilize one of two popular approaches. Types: Single blind → patients don’t know which group they are in ( whether getting drug or placebo). Double blind → neither the patient nor researchers/doctors know which study group the patients are in.

Question 14

What is the purpose of Randomization in an experimental study

Answer 14

process by of assigning patients by chance to groups that receive different treatments

Question 15

Explain the 4 Phases of a cinical trial

Answer 15

PHASE I: Involve testing the new vaccine in adult volunteers, typically fewer than 100. Trial must show successful demonstration of a response on a small-scale (e.g antibody formation in response to vaccine). Rules: Everyone must be healthy, tests for safety, dosage,, and side effects.
PHASE II: expands testing to a group of 100 to 200 subjects, who are selected from the target population for the vaccine, antibody response and clinical reactions to the vaccine are examined. Tests on larger groups of affected individuals, tests for efficacy and side effects.
PHASE III: used to assess protective efficacy in the target population → reduction in incidence rate of a disease in the vaccinated population compared w/ unvaccinated population. Rules: tests on new and wider demographic, tests on long term effectiveness and comparisons w/ other medications. After phase III: testing has been completed, a license to manufacture the vaccine may be granted.
PHASE IV: involve post-marketing research to gather more information about risks and benefits of drug. Rules: Continues to test for effectiveness and safety, can be taken off the market if necessary.

Question 16

Describe the strengths and limitations of an experimental study.

Answer 16

Advantages: provide the greatest control over→ the amount of exposure, the time and frequency of exposure, time period of observation., ability to randomize reduces the likelihood that groups will differ significantly.
Disadvantages: Artificial setting: limited scope of potential impact, adherence to protocol is difficult to enforce, ethical dilemmas.

Question 17

What are the characterisitcs of population based cohort studies

Answer 17

cohort includes either an entire population or a representative sample of the population. ex : Framingham Study (1948), Tecumseh Study (1959), Nurses Health Study (1970s) (Iowa Womens Study (1986), exposures unknown until the first period of observation when exposure information is collected. ex : after clinical assessment, collection of bio samples.

Question 18

What are the charactersitics of exposure based cohort studies

Answer 18

studies overcome limitations of population-based cohort studies, which are not efficient for rare exposures, certain groups, such as occupational groups, may have higher exposures than the general population to specific hazards.

Question 19

What are the characteristics of prospective based cohort studies

Answer 19

purley prospective in nature, characterized by determination of exposure levels at baseline present. Follow up for occurrence of disease for some time→ future.

Question 20

What are the charactersitics of retrospective based cohort studies

Answer 20

make use of historical data to determine exposure level at some baseline in the past.

Question 21

What is an absolute measure of effect

Answer 21

subtract disease frequencies from one another. → Risk Disease: give info about the public health impact of an exposure.

Question 22

What is an relative measure of effect

Answer 22

divide disease frequencies from one another. → Relative Risk, incidence rate ratio, odds ratio: give info about the strength of the relationships between exposure and disease.

Question 23

Provide the relative inforamtion encompassing the 2 by 2 cohort study table

Answer 23

Columns represent disease status or outcome (Y/N) and the rows represent exposure status (Y/N). First column should always refer to those with the disease, and the first row should refer to those with the exposure of interest.
A: ( exposure & disease present) ; B ( exposure present, but no disease); A+B ( total number exposed)
C: no exposure, C ( no exposure, disease present); D ( no disease, no exposure); C+D( total number with no exposure),
A+C ( total number with disease), B+D ( total number without disease), N ( sample total)

Question 24

What is relative risk and how is it intrepreted

Answer 24

: Analysis of cohort and RCT studies: defined as the ratio of the risk of disease ( or death) among the exposed to the risk among the unexposed. Tells you if risk of disease is different among the exposed as compared to the non exposed.
Interpretation of relative risk: RR > 1: the risk of disease among the exposed is GREATER THAN the risk of disease among the non exposed. Exposure could be a risk factor for the disease. RR = 1: → the risk of disease among the exposed is EQUAL to the risk of disease among the non exposed. RR < 1: the risk of disease among the exposed is LESS THAN the risk of disease among the non exposed.

Question 25

What is incidence rate ratio and how it is intrepreted

Answer 25

the ratio of the incidence rate among the exposed to the incidence rate among the unexposed. Tells you if the rate of disease is different among the exposed as compared to the non exposed. Interpretation: IRR > 1: → the incidence rate among the exposed is GREATER THAN the incidence rate among the non exposed. IRR = 1: → the incidence rate among the exposed is EQUAL to the incidence rate among non exposed. IRR < 1: → the incidence rate among the exposed is LESS THAN the incidence among the non exposed.

Question 26

what is risk difference and how is it calculated

Answer 26

difference between the incidence rate of disease in the exposed group and the incidence of disease in the non exposed group. ID’s the # of cases of disease that would be eliminated in the exposed group if the exposure was eliminated.

Question 27

what is the etiologic fraction and what does it tell you

Answer 27

Proportion of the rate of disease in the exposed group that is due to the exposure. Tells you how much the particular exposure accounts for the disease etiology in the exposed group.

Question 28

what is overall incidence rate in the population

Answer 28

Overall incidence rate of disease in a population, made up of 4 components: Ie → incidence rate, Ine → incidence rate in non exposed , Pe → proportion of exposed, Pne → proportion of population non exposed.

Question 29

what is the population risk diffence, how is it calculated, and what's its purpose

Answer 29

Difference between the incidence rate of disease in the non exposed segment of the population (Ine) and the overall incidence rate in the total population (Ip) , → PRD: ( overall incidence rate in population) - (incidence rate in unexposed). Id’s the # of cases of disease that would be eliminated in the total population if the exposure was eliminated. Helps public officials determine which exposures are more important to a given population and helps prioritize prevention activities.

Question 30

Describe the strengths and limitations of a cohort study.

Answer 30

permit direct determination of risk; time sequencing of exposure and outcome; can study multiple outcomes; can study rare exposures. take a long time, costly, subjects lost to follow up ( attraction); selection bias, difficult to use w/ rare diseases.

Question 31

Identify a case-control design by its description.

Answer 31

Type of design that compares persons who have a disease (cases) w/ those who are free from the disease (controls) ; design explores whether differences between cases and controls result from exposures to risk factors. Characteristics: a single point of observation, unit of observation and the unit of analysis are the individual, exposure is determined retrospectively; Does not directly provide incidence data; data collection typically involves a combo of both primary and secondary sources. Steps: 1) determine prevalence/ cases of disease in a N population, pick out healthy control individuals, investigators determine and compare exposures, create 2 by 2. 2) in 2 by 2 table, column totals are first so A+C (disease) and B+D ( no disease) and determine exposures to complete the interior cell totals.

Question 32

what are the applications of case studies

Answer 32

infectious disease outbreak investigation, chronic diseases investigation when etiology is unknown, hypothesis testing.

Question 33

What is the selection of cases process

Answer 33

two tasks are involved in case selection: 1) Defining a case conceptually : Standard diagnostic criteria, severity of the disease. 2) Identifying a case operationally, cases of diseases : who is exposed and who is non exposed. Controls (non diseased): exposed but no diseases and non-exposed and no disease.

Question 34

What is the case selection process

Answer 34

ideally : id and enroll all incident cases in a defined population in a specified time period.

Question 35

How are controls selected

Answer 35

ideal → controls should have the same characteristics as the cases , except exposure of interest. If the controls were equal to the cases in all respects other than disease and the hypothesized risk factor, one would be in a stronger position to describe differences in disease status to the exposure on interest. Cases (diseased) : exposed with disease and exposed w/o disease. Controls: (non-diseased) : exposed w/o disease and not exposed and w/o disease.

Question 36

How are sources of controls determined

Answer 36

population-based controls: obtain a list that contains names and add vessels of most residents in the same geographic area as the cases. Ex: drivers license list, tax lists, voting lists, and telephone directories, patients from the same hospital as the cases: relatives of cases.

Question 37

What formula do case control studies use

Answer 37

Odds ratio

Question 38

How is an odds ratio intrepreted

Answer 38

If OR > 1 Then the odds of disease among the exposed is greater than the odds of disease among the unexposed. So.. it is concluded that the exposure is associated w/ higher odds of disease, or the exposure may be a risk factor for the disease. If OR < 1 Then the odds if disease among the exposed is lower than the odds of disease among the unexposed. So… it is concluded that the exposure is associated w/ lower odds of disease. The exposure may be protective against the disease. Ie: (Exposed) are # times (More/less) likely as (non exposed) to have (disease). The odds of (disease) are #% ( higher/lower) among (exposed) compared to (non-exposed). Express OR as %: If OR > 1 → ( OR -1) *100 = % ( show increased in odds) , If OR < 1 → ( 1-OR) *100% = % (show decrease in odds). “ May the odds be ever in your favor” → WDYM : an OR provides a good approximation of risk when: controls are representative of a target pop., cause are representative of all cases, the frequency of disease in the pop is small.

Question 39

Describe the strengths and limitations of a case-control study.

Answer 39

Tend to use smaller sample sizes than surveys or prospective studies → smaller → more controlled, Quick and easy to complete, cost effective, useful for studies of rare diseases. unclear temporal relationships btwn exposures and diseases : exposures information collected retrospectively → leads to challenges regarding interpretation of results ; use of indirect estimate of risk, not useful for rare exposures, recall bias.

Question 40

Identify a cross-sectional design by its description, what type of study subtype is this

Answer 40

Descriptive ; Surveys of the population to estimate the prevalence of a disease, exposure and disease measures obtained: at the individual level, simultaneously. Single period of observation, Can describe the magnitude and distribution of a health problem. Repeated cross-sectional studies surveys can be used to examine trends in disease or risk factors that vary over time. Applications: to evaluate and compare trends in health and disease, planning, provision, and evaluation of health services: intervention, to identify problems for analytic studies and suggest areas for investigation: hypothesis generation.

Question 41

Describe the strengths and limitations of a cross-sectional study.

Answer 41

Generalizability, conducted in relatively short period of time, low cost limited usefulness for inferring disease etiology, do not provide incidence data, cannot study low prevalence disease, cannot determine temportalty of exposure and disease, exposure and disease info is collected at the same time and after they have occured.

Question 42

Identify an ecologic design by its description.

Answer 42

Unit of analysis in the group, not the individual, makes use of secondary data collected by the government, some other agency, or investigators, level of exposure of each individual in the unit being studied is unknown. In the 2X2 table the interior cell counts are not known. Unit of analysis is the group. Applications of Ecologic Studies: test specific etiologic hypotheses, develop new etiologic hypotheses, suggest mechanisms of causation, identify new methods for disease prevention.

Question 43

Explain how the ecologic fallacy (Simpson’s paradox) could lead to incorrect conclusions about the data.

Answer 43

--> Observations made at the exposure group level may not represent the exposure-disease relationships at the individual level. ecological fallacy occurs when incorrect inferences about the individual are made from group level data. --> means that an association in observed subgroups of a population may be reversed in the entire population. Implications : the conclusions obtained from an ecological study may be the reverse of those from a study that collects data on individual subjects.

Question 44

Describe the strengths and limitations of an ecologic study.

Answer 44

quick, simples, inexpensive, good approach for generation hypotheses when a disease is of unknown etiology. fallacy, imprecise measurement of exposure and disease.

Question 45

What is external validity

Answer 45

implies the ability to generalize beyond a set of observations to some universal statement. A study is externally valid, or generalizable, if it allows unbiased inferences regarding some other target population beyond the subjects in the study.

Question 46

What is internal validity

Answer 46

when there have been proper selection of study groups and a lack of error in measurement. Concerned with the appropriate measurement of exposure, outcome, association between exposure and disease.

Question 47

Discuss the concept of “truth" in the context of epidemiologic associations.

Answer 47

Causation → (Deterministic models of causality) ; Does the association representation a cause-and-effect relationship?

Question 48

Discuss the concept of chance in the context of epidemiologic associations.

Answer 48

Random error → random error ( reflect fluctuations around a true value of a parameter, factors that contribute to random error : poor precision→ occurs when the factor being measured is not measured sharply, , sampling error → arises when obtained samples values (Stats) differ from the values (parameters) of the parent population , variability in measurement → the lack of agreement in results from time to time reflects random error inherent in the type of measurement procedure employed.

Question 49

Discuss the concept of bias in the context of epidemiologic associations.

Answer 49

Systematic error: results in an incorrect (invalid) estimate of the measure of association, error in design, data collection/ analysis, interpretation, reporting, publication, Factors that contribute to bias :observer bias, selection bias, information bias, confounding. Participants’ behavior changes as a result of their knowledge of being observed. Selection bias: arises when the relation between exposure and disease is different for those who participate and those who theoretically would be eligible for study but do not participate. Types: healthy worker effect : employed populations tend to have a lower mortality compared to the general population, important for occupational studies. Looking at one group but not focusing on the other. Information bias: can be introduced as a result of measurement error in assessment of both exposure and disease. Interviewer bias → occurs when interviewers probe more thoroughly for an exposure in a case than in a control. Prevarication (lying) bias: occurs when participants have ulterior motives for answering a question and thus may underestimate or exaggerate an exposure.

Question 50

What is systemic error

Answer 50

results in an incorrect (invalid) estimate of the measure of association, error in design, data collection/ analysis, interpretation, reporting, publication, Factors that contribute to bias :observer bias, selection bias, information bias, confounding. Participants’ behavior changes as a result of their knowledge of being observed.

Question 51

What is selection bias

Answer 51

arises when the relation between exposure and disease is different for those who participate and those who theoretically would be eligible for study but do not participate. Types: healthy worker effect : employed populations tend to have a lower mortality compared to the general population, important for occupational studies. Looking at one group but not focusing on the other.

Question 52

What is information bias

Answer 52

can be introduced as a result of measurement error in assessment of both exposure and disease. Interviewer bias → occurs when interviewers probe more thoroughly for an exposure in a case than in a control. Prevarication (lying) bias: occurs when participants have ulterior motives for answering a question and thus may underestimate or exaggerate an exposure.

Question 53

Identify techniques to reduce random and systematic error at the design and analysis phases of a study.

Answer 53

Develop an explicit (objective) case definition, enroll all cases in a defined time and region, strive for high participation rates, and take precautions to ensure representativeness. Use memory aids; validate exposures, blind interviewers as to subjects’ study status, provide standardized training sessions and protocols, use standardized data collection forms, blind participants as to study goals and classifications status, try to ensure that questions are clearly understood through careful wording and pretesting.

Question 54

List three criteria for a factor to be a confounder.

Answer 54

be a risk factor for the disease, be associated with the exposure, not be an intermediate step in the causal path between exposure and disease.

Question 55

Define confounder

Answer 55

Alternate explanation for observed association between an exposure and disease. A mixing of effects. Association between exposure and disease is distorted because it is mixed with the effect of another factor that is associated with the disease, can be controlled for in the data analysis.

Question 56

Discuss the prevention (design) strategies used to control confounding error.

Answer 56

Randomization , Restriction, matching

Question 57

Discuss the characteristics of randomization as a control of confounding error

Answer 57

attempts to ensure equal distributions of the confounding variables in each exposure category, Advantages → convenient, inexpensive, permits straightforward data analysis. Disadvantages → need to control over the exposures and the ability to assign subjects to study groups, need large sample size.

Question 58

Discuss the characteristics of restriction as a control of confouding error

Answer 58

May prohibit variation of the confounder in the study groups, advantages: provides complete control of known confounders. Disadvantages: unlike randomization, cannot control for unknown confounders. Ex: restricting participants to a narrow age category can eliminate age as a confounder.

Question 59

Discuss the characterisitcs of matching as a control of confounding error

Answer 59

matches subjects in the study groups accounting to the value of the suspected or known confounding variable to ensure equal distributions. Advantages → fewer subjects are required than in unmatched studies of the same hypothesis. Disadvantages → costly

Question 60

Discuss the charactersitcs of stratification as a control of confounding error

Answer 60

analyses performed to evaluate the effect of an exposure within strata (levels) of the confounder. Advantages : performing analyses within strata is a direct and logical strategy, minimum assumptions must be satisfied for the analysis to be appropriate, the computational procedure is straightforward. Disadvantages: small numbers of observations in some strata. A variety of ways to form stata with continuous variables, difficulty in interpretation when several confounding factors must be evaluated. Categorization results in loss of information.

Question 61

Discuss the characteristics of multivariate techniques

Answer 61

through advanced statistical methods (i.e regression analysis), “adjust” for important confounding factors. Advantages: allow for simultaneous adjustment of several confounding variables in a single analysis. Disadvantages: requires more advanced training in statistics.

Question 62

What is a case series

Answer 62

type of medical research study that tracks subjects with similar diagnoses or treatments who have a known exposure Ex. Football players with CTE