Epi Exam 3

In a case-control study of beta-carotene and lung cancer, serum specimens frozen and stored for 20 years are compared between cases and controls. Later it is found that the specimens deteriorated while in storage. Assuming the deterioration led to nondifferential misclassification, how would the resulting odds ratio usually be affected? A. Bias away from the null or overestimation of the true odds ratio B. Bias towards the null or underestimation of the true odds ratio C. No effect on the absolute value of the odds ratio

B.

In a case-control study, which of the following statements about case selection is true? A. Prevalent cases are preferred over incident cases B. Usually selected from among persons seeking medical care for disease under study

B.

Which of the following statements about an epidemiologic cohort study is true? A. External validity is usually not affected by differences between participants and nonparticipants B. Internal validity is usually not affected by differences between participants and nonparticipants C. Both D. Neither

B. Internal validity is usually not affected by differences between participants and nonparticipants

What is the benefit of periodic reexamination or resurvey of the members of the cohort

- Allow for revision of exposure categories - Allow data to be collected on exposures or risk factors that weren't recognized to be of interest at the initiation of the study

Advantages of retrospective cohort over prospective cohort

- Can be completed in a more timely fashion - Less expensive

Goals of Phase IV: Surveillance

- Compare a drug with other drugs already in the market - Often designed to monitor a drug's long-term effectiveness - to measure impact on a patient's quality of life - to determine the cost-effectiveness of a drug therapy relative to other traditional and new therapies

Goals of Phase III: Studies of efficacy

- Determine efficacy in disease of interest - Comparison with other studies of other drugs - Ideal dosage for different patient groups - Experience with multiple investigators

Efficacy

- Evaluation of a treatment among those who receive it - Does it work in ideal situation

Effectiveness

- Evaluation of treatment among those who are allocated to it - Benefit vs. risk

Choices for potential cohort

- General Population - Limited population subgroups a. people in certain industry or occupation b. people from prepaid health plans

Death certificates

- Good for diseases that are frequently fatal - Completely acceptable when total mortality is the end point of interest - far less reliable for cause-specific mortality - additional confirmatory information often obtained from autopsies, physician and hospital records, or next-of kin

Other names for retrospective cohort studies

- Historical cohort study - Historical prospective cohort study - Nonconcurrent prospective study

How does the minimum detectable OR change?

- Moves away from 1.0 as the power increases - Moves away from 1.0 as the level of significance decreases - Moves away from 1.0 as the number of cases and controls decrease - Moves away from 1.0 as the exposure rate among the controls becomes closer to 0 to 1

Choice of study population for cross-sectional studies

- Sometimes selected on the basis of exposure status - Sometimes a sample of people or households or some other unit in a defined geographic area - Once the target population identified, sampling procedures often play a major role by providing for more efficient study designs

Cross-Over Design

- Special case of randomized study - Each subject will receive the intervention and control

What is the goal of randomization

- To balance confounding factors

What causes selection bias

- When an inappropriate control group is chosen - When response rates are either low or unequal for cases and controls

Nature of cross sectional study

- both exposure status and disease status are measured in the study subjects at one point in time or over a short period of time - identified subjects with disease represent prevalent cases becasue we know that they existed at the time of the study buth don't know their duration - disease proportions are determined and compared among those with and without the exposure or at varying levels of exposure

When is blinding not possible

- surgery intervention - behavioral intervention - health care intervention

Procedures to facilitate follow-up

1. Ask each study participant to provide the name and address of an individual who doesn't live with the participant but who is likely to know his or her whereabouts 2. State department of motor vehicles 3. Birth, marriage, and death records 4. Credit bureaus 5. Postal service 6. City directories 7. Physicians offices and records 8. Voter's lists

Disadvantages of matching controls to cases

1. Cannot evaluate differences between cases and controls on matched variables 2. Selection of matched group of controls can be expensive and time-consuming depending on the availability of the matched variables 3. For continuous and ordinal variables, matching categories may be too broad, and residual case-control differences in these variables may persist

Disadvantages of case-control studies within cohorts

1. Case populations cannot be selected until disease status of cohort is known

Selection of Controls: Choice of Group to Use Generally Dictated by:

1. Characteristics and sources of the cases 2. Need to obtain comparable information from cases and controls 3. Practical and economic considerations

Sources of cases

1. Death certificates 2. Autopsy reports 3. Physician records 4. Hospital diagnoses 5. Surgical logs 6. Disease registries 7. Pathology reports 8. Radiology reports 9. Medical reports

Goals of Phase I: Studies of safety and pharmacokinetics

1. Determine maximum tolerated dose 2. Estimate size of Phase II study 3. Determine drug interaction 4. Establish requirments for formulation 5. Dose-response and Administration pharmacodynamic profile

Limitations of cross-sectional study

1. Difficult to separate cause and effect, because it could be hard to determine which happened first 2. A series of prevalent cases will have a higher proportion of cases with disease of long duration than a series of incident cases 3. For diseases with periods of exacerbations and remissions, a person whose disease is in remission may be falsely classified

Strengths of cohort studies

1. Efficient for study of rare exposures 2. Can yield info on multiple exposures 3. Can yield info on multiple outcomes of a particular exposure 4. Clear temporal relationship between exposure and disease 5. Minimizes bias in the ascertainment of exposure 6. Allow direct measurement of disease incidence in exposed and non-exposed groups 7. Strongest observational design for establishing cause-and-effect relationships

Why are external comparison groups not ideal in studies evaluating risks from occupational exposure

1. Employed perons are on average healthier than the general population 2. Exployed have better economic circumstances and improved access to medical care

Disadvantages of using pre-existing records for exposure information

1. Exposure information may be insufficient to address specific research questions 2. Frequently don't contain data on potential confounding variables

When is case-crossover design used for studying etiology of disease

1. Exposure is intermittent 2. Effect on outcome is immediate and lasts only short time 3. Outcome is acute

What you need to do when ascertaining the exposure of risk factors

1. For cases, make sure the risk factor preceded the disease 2. Reduce information bias - use similar procedures for obtaining info from cases and controls 3. Reduce interviewer bias - keep interviewers blinded to specific hypotheses being tested

Phases of Clinical Drug Development

1. Human Pharmacology 2. Preliminary Safety and Efficacy 3. Controlled Trial for Efficacy 4. Post-Marketing Surveillance

Advantages of using case-control studies within cohort

1. If questionnaire data obtained prior to disease development, recall bias is minimized 2. If biospecimens obtained prior to disease development, findings likely represent characteristics present prior to disease development 3. Cost savings 4. Greater comparability between casces and controls

Limitations of Case-Control Studies

1. Inefficient for the evaluation of rare exposures, unless AR is high 2. Can't directly compute incidence rates of disease in exposed and non-exposed individuals, unless study is population-based 3. In some situations, the temporal relationship between exposure and disease may not be difficult to establish 4. Particularly prone to bias compared with other analytic designs, especially selection and recall bias

Measurements of Exposure

1. Intensity 2. Duration 3. Regularity 4. Variability

Disadvantages of Clinical Trials

1. Lack of generalizability 2. Long time for conclusion 3. Large number of participants 4. Financial costs 5. Ethics 6. Subjects may not comply with interventions

Advantages of Using general population controls

1. Less likely to share similar exposures with cases 2. Increase generalizability of study results

Disadvantages of using Hospitalized controls

1. More likely to share similar exposures with cases (potential for biased estimate of effect) 2. Decrease generalizablity of study results

Disadvantage to direct measurements to determine exposure information

1. Need to ensure reliability 2. Basically pertains to the point in time at which the measurement is obtained 3. Time-consuming 4. Expensive

Criteria for selection of matching variables

1. Number should be kept to a minimum 2. Should be potential confounding variables 3. Should be fairly strongly related to the disease 4. Should be readily available at little or no cost to the investigator

Strengths of cross-sectional

1. Often based on a sample of the general population, not just on people seeking medical care 2. Tend to be carried out over a relatively short time period 3. When the current values of the exposure variable are unaltered over time, cross-sectional study data can be used to test epidemiologic hypotheses 4. Can be utilized as cohorts in the future

Nature of Case-control studies

1. Persons with and without disease selected; proportions of each group who have been exposed are determined 2. Began as a response to teh shift from acute to chronic diseases as major public health problem 3. Most frequently undertaken type of observational analytic epidemiologic study 4. Affected by bias more than other study designs, so each must be evaluated individually 5. Compares one case group to one or more control groups

Timeline of Testing of Vaccines

1. Phase 1: Safety and Immunogenicity - small studies, begin in adults 2. Phase 2: Safety, immunogenicity, dose - prospective, randomized, blinded, controlled 3. Efficacy - prospective, randomized, blinded, controlled, size depends on disease attack rate

Monitoring compliance

1. Pill counts 2. Diary 3. Biochemical marker

Disadvantages for conducting interviews and questionnaires of the cohort subjects

1. Potential for recall bias 2. Time-consuming 3. Expensive

The RR you can detect moves further away from the null value as the

1. Power increases 2. Level of significance decreases 3. Expected number of cases decreases

Ways to obtain probability samples of the population

1. Random digit dialing 2 Canvassing households in targeted neighborhoods 3. Population registers such as voting lists, driver's licesnse tapes, ect.

Advantages of Clinical Trials

1. Randomization - balance of confounding factors 2. Uniform collection of data 3. Protocol procedures and interventions specified 4. Blinding 5. Statistical comparison based on statistical theory

Strengths of Case-Control Studies

1. Relatively quick and inexpensive compared with other analytic designs 2. particularly well-suited to the evaluation of diseases with long latent periods 3. Optimal for the evaluation of rare diseases 4. Can examne multiple etiologic factors for a single disease 5. Generally require a smaller number of subjects

Other names for: 1. Case-control study 2. Cohort study 3. Prospective cohort study 4. Retrospective cohort 5. Randomized trial 6. Cross-sectional

1. Retrospective study 2. Longitudinal study, prospective study 3. Concurrent cohort/concurrent prospective 4. Historical cohort/nonconcurrent prospective 5. Experimental study 6. Prevelence Survey

Goals of Phase II: Studies of safety and efficacy trends

1. Screen drug for possible activity 2. Establish incidence of side effects 3. Establish trends in efficacy 4. Define appropriate dosage schedule 5. Provide pharmacological, pharmacodynamic and metabolic data

Approaches to Sampling Controls in Hospital-based studies

1. Select controls from a variety of different diagnostic groups, so no particular risk factors will be overrepresented 2. Select controls from patients with acute conditions, so earlier exposures couldn't have influenced by condition 3. Don't select patients with multiple concurrent conditions 4. Don't select patients with diagnoses know to be related to the risk factor of interest

Measures to increase compliance in clinical trials

1. Selection of participants 2. Run-in period 3. Dispensing device 4. Frequent contact 5. Medical monitoring

Diagnostic Criteria

1. Should be defined before the study begins to ensure that the determination of presence or absence of disease be made in a uniform manner for exposed and unexposed cohort members 2. Their nature varies depending on the outcomes of interest and the metods used to identify disease 3. If information on cause of death from death certificates is supplemented by other sources of information, clear criteria must e established as to which sources of data have precedence in assigning cause of death 4. The person(s) assigning the outcome should be blinded to the exposure status of the cohort member

Reasons for noncompliance in clinical trials

1. Side effects 2. Difficulty of intervention 3. Forgetting 4. Withdrawal 5. Crossover 6. Moving

Ways to improve the quality of a cross-sectional study

1. Time of onset of first symptoms of disease should be determined 2. For diseases with periods of exacerbation and remission, important to ask people currently without signs or symptoms whether they have had such symptoms in the past 3. Diagnostic criteria need to be established, preferably in advance

Limitations of cohort studies

1. Time-consuming and expensive, especially if prospective 2. If retrospective, require the availability of adequate records 3. Often requires a large sample size 4. Inefficient for the evaluation of rare diseases, unless the attributable risk is high 5. Validity of the results can be seriously affected by loses to follow-up 6. Changes over time in diagnostic methods may lead to biased results

How are biospecimens used in research?

1. To evaluate the role of genetics in disease development, treatment effectiveness, outcome 2. Support basic, epidemiologic, translational, and clinical research at molecular level 3. Can be combined with environmental data to evaluate gene-environment interactions

Matching Controls to Cases Advantages

1. Understood by people with little background in statistics 2. Control confounding variables that are difficult to measure directly 3. May eliminate the need to assemble a comprehensive list of all eligible controls 4. May provide a more appropriate nonhospitalized or hospitalized control group for comparison with hospitalized cases 5. Can provide for more adequate control of confounding by continuous variables than can adjustment in the analysis 6. Potential gain in accuracy of estimating the odds ratio

Advantages of using pre-existing records for exposure information

1. Usually available for a high proportion of the cohort 2. Relatively inexpensive to obtain 3. Unbiased classification of exposure status

Disadvantages of using general population controls

1. Usually more costly and time-consuming than hospital controls 2. Population lists from which to select not always available 3. May not recall exposures with the same level of accuracy as cases 4. May be less motivated to participate

From the population-based breast cancer case-control data presented in the table below, what is the most appropriate estimate of the prevalence of singles in the study population? Marital Status | Cases | Controls | Total Single | 20 | 20 | 40 Married | 80 | 180 | 260 Total | 100 | 200 | 300 A. 0 - 10% B. 11 - 20% C. 21 - 30% D. 31% or greater E. Cannot be calculated from the data given

A

From the population-based breast cancer case-control data presented in the table below. The breast cancer incidence rate in the population of interest is 5%. Calculate the attributable risk for being single Marital Status | Cases | Controls | Total Single | 20 | 20 | 40 Married | 80 | 180 | 260 Total | 100 | 200 | 300 A. 0 - 25% B. 26 - 50% C. 51 - 75% D. 76 - 100% E. Cannot be calculated from the data given

A

Strengths of cross-sectional studies include A. Can be utilized as the starting point for a prospective cohort study B. Tend to be carried out over a long time period C. Both D. Neither

A

Clinical Trial Definition

A planned experiment designed to assess the efficacy of a treatment in man by comparing outcomes in a group of patients treated with the test treatment with those observed in a comparable group of patients receiving a control treatment, where both groups are enrolled, treated, and followed over the same period of time

Internal Comparison Group

A study cohort is chosen and divided by exposure assessment into exposed and non-exposed groups

- Time to develop a drug? - Cost to develop a drug? - Cost to develop a biologic? - How many new medicines approved by FDA in 2014?

A. 10-15 years B. 1,318 million C. 1.2 billion D. 51 new medicines: 27 new drugs

In a cohort study of hormone replacement therapy (HRT) and risk of coronoary heart disease (CHD), high income level is associated with both HRT and CHD. In this cohort study high income is best classified as representing A. Confounding bias B. Differential misclassification C. Nondifferential misclassification D. Recall bias E. Selection bias

A. Confounding bias

Most desirable vs. most common way of obtaining cases

A. Desirable: Include all incident cases in a defined population over a specified period of time B. Common: Select all incidence cases seen at certain hospitals over a specified period of time

The population attributable risk % A. Equals the attributable risk % when the prevalence of exposure is 100% B. Is always greater than the attributable risk % unless the prevalence of exposure is 100% C. Both D. Neither

A. Equals the attributable risk % when the prevalence of exposure is 100%

Meaning of different values of OR

A. OR = 1.0 indicates odds of exposure are identical in case and control groups (no association) B. OR > 1.0: increased odds of exposure among cases as compared to controls (harmful exposure effect) C. OR < 1.0: decreased odds of exposure among cases as compared to controls (protective exposure effect)

Types of Bias in Case-Control Study

A. Selection Bias B. Information Bias 1. Recall bias 2. Interviewer bias

Different type of biases

A. Single blind: blinding of study subjects B. Double blind: blinding of observers C. Triple blind: blinding of staticisions, monitors

The relative risk is the comparison of A. Two incidence rates B. Two prevalence rates C. Both D. Neither

A. Two incidence rates

Selection of cases

A. Usually selected from among people seeking medical care for disease under study B. Newly diagnosed cases preferred 1. If study subject had disease for a long period of time, it could be difficult to distinguish exposures the caused disease 2. Prevalent cases can lead to an overrepresentation of cases with long duration (possible survival bias) C. Diagnostic criteria should be established - usually based on info routinely available in medical record

Matching of controls to cases: Confounding

A. When present, the primary determinant of the magnitude of the difference in accuracy for a matched compared to an unmatched odds ratio is the magnitude of the association between the confounding variable an the disease under study B. Matching for a variable that isn't a confounder can lead to a sizable loss in accuracy, especially when the variable is unrelated to disease but strongly related to the exposure

Attributable Risk Values association affects

AR = 0: no exposure AR > 0: Harmful exposure effect AR < 0: Protective exposure effect

Advantages of using Hospitalized controls

Advantages 1. Easily identified and readily available in sufficient numbers 2. More likely than healthy individuals to e aware of antecedent exposures or events (reduce recall bias) 3. More likely to hae been subject to same intangible selection factors as the cases using that hospital 4. More likely to be willing to cooperate than healthy individuals (reduce nonparticipation bias)

Advantage of conducting interviews and questionnaires for the cohort subjects

Allows for data collection on exposures that are not routinely recorded

Odds Ratio Defn

An estimation of the relative risk obtained by calculating the ratio of the odds of exposure among cases compared to control

Surrogate Outcome

An outcome, based on some test or measurement, that is used instead of a clinical event in the design or analysis of a clinical trial

What question does pragmatic trials answer?

Answers questions about the overall effectivenss of an intervention and cannot study the contributions of its different components

From the population-based breast cancer case-control data presented in the table below, what is the population attributable risk percent? Marital Status | Cases | Controls | Total Single | 20 | 20 | 40 Married | 80 | 180 | 260 Total | 100 | 200 | 300 A. 0 - 10% B. 11 - 20% C. 21 - 30% D. 31% or greater E. Cannot be calculated from the data given

B

In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that A. At the beginning of the study, those with the disease and those without the disease have equal risks of having the factor B. Exposure to the suspected factor occurs prior to the development of disease C. The study group with the factor and the study group without the factor be representative of teh general population D. The suspected factor be a risk factor for the disease E. There be equal numbers of persons in both study groups

B

Selection bias

Can occur whenever the inclusion of cases or controls into the study depends in some way on the exposure of interest

Factorial Designs

Comparison of the combination of several interventions

Types of Clinical Trials: Historical Controls

Comparison with results from prior conventional treatment

Types of Clinical Trials: Nonrandomized Study

Concurrent study with nonrandom assignment of treatment

Types of Clinical Trials: Randomized Study

Concurrent study with randomized assignment of treatment

External Comparison Group

Consists of the general population from the area from which the exposed group is obtained

What is a nonrandomized study

Controls and intervention subjects are entered, treated and followed at approximately the same time. Allocation is by a non-random process

An unmatched case-control study is conducted evaluating folic acid nutrition and congenital defects. Maternal folate deficiency was found in 15 of 100 mothers of cases and 10 of 200 mothers of controls. What is the odds of exposure (folate deficiency) among mothers of cases A. 10/200 B. 10/190 C. 15/100 D. 15/85 E. 15/10

D.

Controls are needed in a case-control study because A. They are matched to teh cases for suspected etiologic factors B. They increase the sample size, so that statistical significance may be achieved C. They may be followed to determine if they develop the disease in question D. They provide a comparable estimate of the frequency of exposure in the absence of time E. They reduce bias

D.

In a randomized trial, a planned crossover design: A. Eliminates the need for monitoring compliance and noncompliance B. Eliminates the problem of a possible order effect C. Enhances the generalizability of study results D. Must take into account the problem of possible residual effects of the first therapy E. Requires stratified randomization

D.

The odds ratio is the comparison of A. Two incidence rates B. Two prevalence rates C. Both D. Neither

D.

Advantage of a direct measurement for exposure information (lab results, physical exam, ect)

More accurate classification

Type II Error

Not finding a difference when one actually exists; failing to reject the null that is actualy false

Odds Ratio formula

OR = ad/bc a = number of exposed cases b = number of exposed controls c = number of nonexposed cases d = number of nonexposed controls

Matched sampling

Pairing of one or more controlsto each-case on the basis of specific variables

Attricutable Risk Definition

Quantifies the risk of disease in the exposed group that can be considered attributable to the exposure by removing the risk of disease that would have occurred anyway due to other causes

Relative Risk

Ratio of the measures of disease frequency for two populations RR = Ie/Io

Differential or nonrandom misclassification

Results in a biased risk estimate that is either an underestimate, an overestimate, or the same as the true measure of association

Stratified sampling

Selection of individuals at random from defined subgroups of the target population

Systematic sampling

Sequential selection of individuals

In a study in which all cases of a disease that developed were ascertained, if the relative risk for the association between a factor and the disease is equal to or less than 1.0, then A. Either matching or randomization has been unsuccessful B. The comparison group used was unsuitable yielding an invalid comparison C. The factor protects against the development of the disease D. There is either no association or a negative association between the factor and the disease E. There is no association between the factor and the disease

D. There is either no association or a negative association between the factor and the disease

Attributable Risk Definition

Difference between the incidence rates in the exposed and non-exposed groups

Measures to increase compliance in a clinical trial include each of the following except: A. Dispensing device B. Frequent contact C. Medical monitoring D. Run-in period E. Use of a placebo

E

The population-based breast cancer case-control data presented in the table below, calculated the attributaale risk for being single Marital Status | Cases | Controls | Total Single | 20 | 20 | 40 Married | 80 | 180 | 260 Total | 100 | 200 | 300 A. 0 - 25% B. 26 - 50% C. 51 - 75% D. 76 - 100% E. Cannot be calculated from the data given

E

A randomized clinical trial was designed to compare two different treatment approaches for asthmatic attacks. A purpose of randomization in this study was to A. Decrease misclassification bias B. decrease the likelihood that observed differences in clinical outcomes are due to chance C. Increase patient compliance with treatment D. Obtain treatment groups of similar size E. Obtain treatment groups with comparable baseline characteristics

E.

A small clinical trial is designed to compare the effectiveness of a new treatment versus standard treatment for non-Hodgkin lymphoma. No difference in 5-year survival percentage is observed despite the fact that, in truth, the new treatment is superior. The failure to detect a benefit for the new treatment is best described as A. Blinding B. Observer bias C. Placebo effect D. Type I error E. Type II error

E.

The major purpose of random assignment in a clinical trial is to: A. Ensure the study groups have noncomparable baseline characteristics B. Facilitate double blinding C. Facilitate the measurement of outcome variables D. Help ensure the study subjects are representative of the general population E. Reduce selection bias in the allocation of treatment

E.

Information Bias

Errors obtained from subjects once they have been entered into the study

Effects of nonparticipation

External validity (generalizability) of study results is affected by differences between participants and nonparticipants

True or False: Internal validity of study results is usually affected by differences between participants and nonparticipants

False

True or False: OR is based on concordant pairsr

False. OR is based on discordant pairs

Attributable Risk

Ie - Io Can be calculated if incidence rates can be estimated among exposed and nonexposed groups

What would make the risk estimate of the true relationship between exposure and disease biased

If non-response is related to both the exposure and, independent of the exposure, to the outcome under study

Ascertainment of Exposure to Risk Factor

If the control group is over-represented with exposed persons, the OR for disease of interest will be underestimated. If control group is underrepresented with exposed persons, OR will be overestimated

Non-random misclassification

If the proportion of inaccurate responses differ in both study groups, resulting in bias with a direction that is either more or less extreme than the true association

Underestimation of the true association

If the proportion of inaccurate responses is the same in both study groups, then the effect of such random misclassification will only minimize the differences between the groups

Biases of particular concern in case-control study

Both recall and selection

Rather than their exposure status, how are groups for cohort studies usually chosen

By their ability to facilitate the collection of relavent information (i.e. doctors, nurses, union members, students at a certain university, ect)

Each of the following statements about retrospective cohort studies is true except: A. Incidence rates may be computed B. Recall bias is minimized C. The required sample size is smaller than that needed for a prospective study D. The study groups are often exposed and nonexposed E. Theya re useful for rare exposures

C

In a cross-sectional study A. Prevalence of disease can be compared in exposed and non-exposed B. Prevalence of exposure can be compared in diseased and non-diseased C. Both D. Neither

C

The case subject serves as his/her own control in which of the following study designs? A. Case-cohort study B. Case-control study C. Case-crossover study D. Prospective cohort study E. Retrospective cohort

C

In a case-control study of beta-carotene and lung cancer, serum specimens frozen and stored for 20 years are compared between cases andcontrols. later is found the specimens deteriorated while in storage. assuming the deterioration affected beta-carotene levels this could lead to A. Confounding bias B. Differential misclassification C. Nondifferential misclassification D. Recall bias E. Selection bias

C.

In a clinical trial comparing medical and surgical treatment of duodenal ulcers, 20% of the patients randomized to medical treatment ultimately underwent a surgical procedure whereas 10% of the patients initially assigned to surgery later required additional medical management. Analysis of this study according to initial treatment allocation, ignoring subsequent change in therapy, is best described as A. Blinding B. Compliance C. Intention to treat D. Observer bias E. Placebo effect

C.

Description of Retrospective cohort studies

The investigator identifies a cohort of individuals based on their characteristics in the past and then reconstructs their subsequent disease experience up to some defined point in the more recent past

Nature of Prospective Cohort Studies

The investigator starts with a group of individuals apparently free of disease(s), divides them into those exposed to a possible factor and those not exposed, and then follows them forward through time in order to determine the incidence (or mortality) rate among the exposed and incidence (or mortality) rate among the unexposed

Population Attributable Risk Percentage

The percentage of disease or death in the population that is attributable to an exposure

Purpose of Therapeutic Trials

To cure or alter the course of disease

Purpose of Preventative Trial

To prevent the occurrence of a risk factor or to alter the risk factor to prevent occurrence of disease

True or False: Magnitude of the relative risk does not predict the magnitude of the attributable risk

True

What question is case-crossover answering?

Was this event triggered by something unusual that happened just before?

Nondifferential or random misclassification

When inaccuracies exist in the categorization of subjects by exposure or disease status but these inaccuracies occur in similar proportions in each of the study groups (underestimate true risk)

Rare disease assumption

When the disease is rare the total number exposed can be approximated by the number of exposed controls and total unexposed by the number of non-exposed controls

What is a Historical Control Study?

a new intervention is used in a series of subjects and compared to the outcome from a prior series

Biospecimens defn

biological materials collected from people

Random sampling

each eligible subject has fixed and equal probability of selection

True or False: Potential for selection bias is less of a concern in cohort than in case-control studies

true

Pragmatic Trials

used to test an overall package of care, including the contribution of the therapeutic relationship, patients' expectations, and any specific therapy that is used