Exam 2 Flashcards
Ecologic Studies
- unit: group level
- can be used for making hypothesis
- level of exposure for each individual is unknown
- uses secondary data
ecologic comparison study
assess the correlation between exposure rates and disease rates among different groups over the same time period
ecologic trend study
- correlation of changes in exposure with changes in disease within the same community, population, etc
Ecologic Fallacy
- occurs when incorrect inferences about the individual are made from group-level data.
- observations made at the group level may not represent the exposure-disease relationship at the individual level
advantages and disadvantages of ecologic studies
- advantages:
- quick, simple, inexpensive, good for
generating hypotheses when a disease is
of unknown etiology
- quick, simple, inexpensive, good for
- disadvantages:
- ecological fallacy, imprecise measurement
of exposure and disease
- ecological fallacy, imprecise measurement
cross-sectional study
- aka prevalence study
- exposure and disease measures done at the individual level
- Single period of observation
- Exposure and disease histories are collected simultaneously.
- Both probability and non-probability sampling are used
limitations of cross-sectional studies
- Can’t really infer disease etiology
- Doesn’t have incidence data
- Can’t study low-prevalence diseases
- Can’t determine the time between exposure and disease
cross-sectional survey strengths
- Studies several associations at once
- Takes a short period of time
- Produce prevalence data
- Biases due to observation (recall and interviewer bias) and loss to follow-up do not exist
- Can provide evidence of the need for analytic epidemiologic study
types of data
- nominal
- ordinal
- discrete
- continous
nominal data
- categorical: unordered categories
- two levels: dichotomous
- more than two levels: multichotomous
- examples: sex, disease (yes, no), race, marital status, education status
ordinal data
- categorical: ordering informative
- examples: preference rating (agree, neutral, disagree)
discrete data
- quantitative: integers
- example: number of cases
continuous data
- quantitative: values on a continuum
- examples: dose of ionizing radiation
crude vs age-adjusted rates
- The crude rate is calculated without restrictions, such as by age or sex, or who is counted in the numerator or denominator.
- These rates are limited if we try to compare them between subgroups of the population or over time because of confounding influences, such as differences in age distribution between groups.
numerical methods
- measures of central tendency
- measures of dispersion
measures of central tendency
- mean: average of a set of values
- median: middle number in a sorted list of numbers
- mode: value that appears the most frequently in a data set
measures of dispersion
- range
- inter-quartile range
- variance
- standard deviation
- coefficient of variation
- empirical rule
- Chebychev’s inequality
experimental studies
- aka intervention studies
- investigators influence the exposure of subjects
- 2 types: controlled trials, community trials
Within-group design
- the outcome in a single-group is compared before and after the intervention
- strengths: individual characteristics that confound an association are controlled
- weakness: susceptible to confounding from time-related factors such as the media
controlled trial
- unit of analysis is the individual
- randomized controlled trial in a clinical setting is called a clinical trial
natural experiment
- researchers don’t assign subjects unlike controlled
- assignment into treatment and control is random like controlled experiments
- researchers don’t design/ administer treatment unlike controlled
- ex: John Snow cholera experiment
Between-group design
- comparison between 2 outcomes observed in 2 or more groups of subjects that get different levels of intervention
within-group design
- compare the outcomes observed in a single group before and after the intervention
Advantages of Randomized Controlled Clinical Trials
- eliminate conscious bias due to physician or patient selection
- averages out unconscious bias due to unknown factors
- groups are “alike on average”
Disadvantages of Randomized Controlled Clinical Trials
- ethical issues
- interferes with doctor-patient relationship
single-blind study
- subjects are blinded, but investigators are aware
- ex: placebo controlled study
double-blind study
- subjects and investigators don’t know who is in what group
triple-blind study
- treatment and research approaches kept a secret from subject and investigators
- analyses are done by a separate party removed from investigators
Why are patients blinded?
- patients try to get well/ please physicians
- minimize potential bias from the placebo effect
Placebo effect
- effect of patient outcomes that may occur due to the expectation by a patient that the intervention will work
problems with blinding patients
- for non-drug studies like behavior change or surgeries it may be impossible or unethical to blind
- may be problematic in drug studies where treatment has a characteristic side effect
strengths of blinded randomized controlled clinical trials
- shows cause and effect
- faster and cheaper than observation studies
- investigators can control exposure levels
- only appropriate approach for some research questions
weaknesses of blinded randomized controlled clinical trials
- often costly in time and money
- research questions are not suitable for experimental design due to ethics and rare outcomes
- many research questions are not suitable to blinding
- limited generalizability due to volunteers’ eligibility
Phase 1 trial
- unblinded, uncontrolled study with fewer than 30 patients
- purpose is to determine safety
- patient usually have advanced disease and tried other options
- often undergo intense monitoring
Phase 2 trial
- up to ~50 people randomized blinded trials
- tests: tolerability, safe dosage, side effects, how the body reacts to drug
- evaluate which types of disease a treatment is effective against and most effective dosage
Phase 3 trial
- thousands of patients
- random assignment of treatment
- dosage and methods of administering are evaluated
Phase 4 Trial
- large study after FDA approval
- assess the rate of serious side effects and explore further therapeutic uses
what is a clinical trial?
research that test medical or health-related interventions
what does phase 1 and 2 trials test?
the safety and effectiveness of the intervention
what does a phase 3 trial test?
if the intervention works and is it helpful
what is included in the experimental arm?
the group that gets the new treatment
what is included in the control arm?
the group that gets the usual care
what does randomized mean?
the decision to assign a subject to a group is done completely by chance
informed consent
researcher provides all information related to the study to participants (ex: risks of treatment)
when conducting research you should avoid what in terms of voluntary participation?
using pressure and coercion to get people to participate if they wouldn’t do it on their own
what does honesty and integrity mean in terms of research ethics?
honestly reporting findings
plagiarism
not asking for permission before using other materials
in the 1930’s how many American’s were affected by syphilis?
1 out of 10
what were the 2 key questions that healthcare professionals had during the syphilis experiment?
- did late-stage syphilis warrant the risks of existing treatments
- did the individual’s race affect how syphilis progressed
what was the lie the syphilis study was based on?
participants were told they are getting free drugs and care when they weren’t
What happened in Guatemala in the 1940’s?
non-infected individuals were infected with sexually transmitted infections
when did the syphilis experiment end?
1972
what was found at the end of syphilis experiment?
no evidence that race impacted how the disease progresses was found (found nothing)
