epidemiology exam 2 5-8 Flashcards
what is secular trend
changes in frequency over time
what is a population pyramid and how is it changing the U.S over time. What implications does this have on public health.
has been used for many years by demographers and epidemiologists to track and compare changes in population age distribution over time.
how is it changing the U.S over time = affected by birth rates and fertility levels ,wars and death rates and migration
implications does this have on public health - approximately 20 percent of the U.S population in 2030 will be age 65 or older
the need for health aging related services will grow
characteristics to describe a population
nativity and migration
religion
socioeconomic status
age
sex
marital status
race and ethnicity
reasons for age associations
diagnoses across the life span
multimodality of trends
latency effects
action of the human biologic clock
life cycle and behavioral phenomena
diagnoses across lifespan
Some infections (e.g., mumps and chickenpox) occur more commonly during childhood.
The leading cause of death among young adults is unintentional injuries.
Maternal age is associated with rates of diabetes and related complications.
The incidence of and mortality from chronic diseases increase with age.
Age-specific incidence rates among elderly often inaccurate. Multiple sources of morbidity may afflict a single elderly individual.
multimodality
Age-specific distributions can be linear (e.g., cancer), or multimodal (e.g., tuberculosis).
latency effects
Age effects on mortality may reflect the long latency period between environmental exposures and subsequent development of disease.
biologic clock phenomenon
Waning of the immune system may result in increased susceptibility to disease, or aging may trigger appearance of conditions believed to have genetic basis.
sex differences: female Paradox 1970
female age-standardized morbidity rates for many acute and chronic conditions were higher than rates for males, even though mortality was higher among males.
coronary heart disease
leading cause of death in mortality among women
Less alert; Less seek treatment (often seen as stress)
Gender bias from medical professionals when seeking treatment, underdiagnosing and undertreating
place examples
address where health related states or events are occurring the most or frequently
involves comparisons between or among geographic regions in groups before or after mirgration
reasons of place variation in disease
Gene/environment interaction
Examples: sickle-cell gene
Influence of climate
Examples: Yaws, Hansen’s disease
Environmental factors
Example: chemical agents linked to cancer
what is time
aspects of the epidemiologic investigations range from hours to weeks from years to decade
characteristics of time
cyclic fluctuations (seasonal trends )
point epidemics ( short term)
secular time trends ( trend over the years )
clustering - temporal or spatial
point epidemics
response of a group of people circumscribed in place and time to a common source of infection, contamination, or other etiologic factor to which they were exposed almost simultaneously.
Examples:
foodborne illness
responses to toxic substances –Love Canal
infectious diseases
love canal
became a symbol of the dangers of toxic waste in residential neighborhoods the legal and medical issues that are still playing out
They dumped the chemicals in the canal in Nigeria falls, people who lived close started to smell the different chemicals and children started to obtain skin rashes.
some people were able to relocate into different homes but others had to stay and had trouble relocated
case clustering
refers to an unusual aggregation of health events grouped together in space and time.
temporal clustering
post-vaccination reactions, postpartum depression.
spatial clustering
concentration of disease in a specific geographic area, e.g., Hodgkin’s disease.
secular time trends
is the general systematic linear or nonlinear component that changes over time and it represents the long term changes in health related states or events
aging population, which tends to have different spending and savings habits than a younger population
cyclic fluctuations
periodic fluctuations on an annual or other basis. epidemic disease outbreaks – short-term fluctuations. Time trends contribute to our understanding of the natural history of epidemics of acute infectious diseases such as measles or waterborne disease, as well as NCDs such as stroke or cancer.
examples of disease specific health status indicators
global or life expectancies
fertility rate
death rates
examples of non disease indicators
health disparities and demographic and social variables
global burden - disability adjusted life year
combines information on mortality with information on morbidity for specific causes.
life expectancy
refers to the number of years an individual is likely to live
years of potential life lost
Measure of premature mortality or early death
Recognizes that death occurring in the same person at a younger age involves a greater loss of productive years
If YPLL is high, that reflects that younger persons are dying from the disease
Improvements in life expectancy can cause the increase in an available work force which, in turn, benefits society by increased productivity.
crude death rate
A summary rate based on the actual number of events (in this case death) in a population over a given time period. It approximates the proportion of the population that dies during a time period of interest
age specific rate
Frequency of a disease in a particular age stratum divided by the total of number of persons within that age stratum during a time period.
infant mortality rate
Number of infant deaths among infants age 0-365 days during a year divided by a number of live births during the same year (expressed as the rate per 1,000 live births
age adjusted standardized rate
Used to control for the changing age distributions of the population, and; therefore, they make important death comparisons of vital rates over time and between age groups. This is the total expected number of deaths divided by the total estimated population (in a specific year) times 100,000.
Direct-Method of Adjustment
This adjustment method may be used if age-specific death (or other health event) rates in a population to be standardized are known and a suitable standard population is available.
Indirect-Method of Adjustment
This method is used if age-specific death rates of the population for standardization are unknown or unstable (e.g., because the rates to be standardized are based on a small population).
Standardized mortality rate (SMR)
This is calculated by dividing the observed deaths by expected deaths and multiplying that calculated number by 100
Cause-Specific Rate
A rate that specifies events, such as deaths according to their cause. It is divided by the total population, in a time period.
Proportional mortality rate (PMR)
The number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population.
Maternal Mortality Rate
The number of maternal deaths ascribed to childbirth (i.e., pregnancy and puerperal causes) per 10,000 or 100,000 live births.
Neonatal Mortality Rate
Measures the risk of dying among newborn infants who are under the age of 28 days (0-27) for a given year.
crude birth rate
refers to the number of live births during a specific period of time per the resident population during the midpoint of the time period
Useful measure of population growth and a index for comparison of developed and developing countries
General Fertility Rate
This rate consists of the (number of live births reported in an area during a given time interval) divided by (the number of women aged 15-44 years in that area)
health indicator
is a marker of health status physical or mental disease ,impairments or disability and social well being or service provision or resources availability
Males have a higher all-cause-age-specific and age-adjusted mortality rate than females from birth to 85+.
true
what are variables that related to community health
environmental variables
Air pollution from stationary and mobile sources
Access to parks/recreational facilities
Availability of clean water
Availability of markets that supply healthful groceries
Number of liquor stores and fast-food outlets
Nutritional quality of foods and beverages vended to school-children
what are descriptive studies
uses observational studies of the distribution of disease in terms of person, place, and time.
analytic studies
evaluate one or more predetermined hypothesis about associations between the exposure and outcome variables
what is hypothesis generating
the researcher explores a set of data searching for relationships and patterns, and then proposes hypotheses which may then be tested in some subsequent study.
hypothesis testing
conducting statistical tests to estimate the probability that the observed differences were simply due to random error
what is the purpose of health people 2020
attain high-quality, longer lives free of preventable disease, disability, injury, and premature death; achieve health equity, eliminate disparities, and improve the health of all groups; create social and physical environments that promote good health for all
measures that adjust for difference in age
crude death rate - calculated without any restrictions, such as by age or sex
These rates are limited because of potential confounding influences during comparisons, such as differences in the age-distribution between groups.
age adjusted rate -a weighted average of the age-specific rates, where weights are the proportions of persons in the corresponding age groups of a standard population.
direct adjustments
use when age-specific rates are available
Removes the affects of age on rates in two different population
Apply actual age-specific rates to a standardized population (US population 2000
indirect adjustments
when age-specific rates are not available or are unstable
age specific rate
the number of cases per age group of population during a specific time period
formula - RI = number of deaths among those age 5-14 / number of persons who are 5-14 years during the time periodtimes 100,000
standardized mortality ratio
SMR= observed deaths / expected deaths times 100
familiar with measures related to mortality and their applications
infant mortality rates - formula - number of infant deaths infant as 0-365 days / number of live birth during the year
crude mortality rate - population from which the deaths occurred
cause specific mortality rate - population from which the deaths arise
age specific mortality rate - includes all death in a specific age group and the total population in the specific age group
proportionate mortality rate - denominator number of deaths in the same time period
neonatal mortality rate - number of live births in the same time period
post neonatal mortality rate- number of live births in the same year
perinatal mortality rate -number of stillbirths plus live birth
maternal mortality rate- number of live births in the same time period
what are the measures of health disparities and income inequalities
income inequality - if the home income inequality is low then an increase in the slope will lead to a relatively small increase in health disparities between the rich and the poor.
characteristics of a good study design
Enable comparison between two or more groups
Allow the comparison to be quantified (absolute or relative)
Assess temporal sequence
Minimize biases, confounding, and error
how do study designs differ
Number of observations made
2.Directionality of exposure
3.Data collection methods
4.Timing of data collection
5.Unit of observation (analysis)
6.Availability of subjects
. What are characteristics of analytical studies?
experimental studies -Randomized
Control
(Intervention)
Trials
observational studies- cohort ,case control and cross sectional
difference between observational and experimental
that a well-done observational study does not influence the responses of participants
experimental -do have some sort of treatment condition applied to at least some participants by random assignment.
observational
descriptive - case reports and series .ecological studies ,cross sectional studies
analytic - case control and cohort
experimental
randomized control trails and others before and after studies and non randomized trails
what is quasi and experimental
experiment is a study in which the researchers manipulates the level of some independent variable and then measures the outcomes
quasi-Most community-based trials
Less rigorous than RCTs
Unable to randomly assign
Contamination issues
Involves external control without randomization
cross sectional example senario
medical study examining the prevalence of cancer amongst a defined population using surveys or questions more observation and descriptive
case control example scenario
medical researchers study disease x and use a case control to identify the factors
cohort studies scenario
if researchers hypothesize that exposure to a chemical increases skin cancer, they can form a cohort based on exposure to that chemical
Then they follow the cohort and assess cancer rates relative to a comparison group without the exposure
what are case control studies
with two groups, one group has the disease of interest (cases) and a comparable group is free from the disease (controls)
possible causes of disease by finding out how the two groups differ with respect to exposure to some factor
characteristics of case control study
A single point of observation (single point in time)
Defined by presence or absence of the outcome
Exposure is determined retrospectively
Does not directly provide incidence data
how do we determine the best controls
Population-based controls
Patients from the same hospital as the cases
Relatives of cases (e.g., sibling, twin)
Friends of cases–SES control
what is the best measure of association for case control studies
odds ratio - the odds of exposure to a factor among cases divided by the odds of exposure to a factor to factor among controls
odds ratio vs relative risk when does the odds ratio approximate RR
When the risks (or odds) in the two groups being compared are both small (say less than 20%
Disease is rare
Controls are representative of target population
Cases are representative of all cases
calculate an odds ratio
odds of the event in the exposure group (a/b) divided by the odds of the event in the control or non-exposure group (c/d).
examples of case control studies and the advantages and limitations
example - is migraine headache associated with concussion in Athletes
advantages -Tend to use smaller sample sizes than surveys or prospective studies
Quick and easy to complete
Cost effective
Useful for studies of rare or unusual diseases
limitations-
Provide indirect estimate of risk
Timing of exposure-disease relationship difficult to determine
Representativeness of cases and controls often unknown
what is temporality
refers to the timing of information about cause and effect.
prospective cohort study
Purely prospective in nature; characterized by determination of exposure levels at baseline (the present), and follow-up for occurrence of disease at some time in the future.
advantages -Enable the investigator to collect data on exposures; the most direct and specific test of the study hypothesis.
The size of the cohort is under greater control by the investigators.
disadvantages -long follow-up period while waiting for events or diseases to occur.
variable to a high loss rate
retrospective cohort study
make use of historical data to determine exposure level at some baseline in the past
.advantages -less expensive to perform than cohort studies and they can be performed immediately because they are retrospective
limitation - poor control over the exposure factor covariates and potential confounders
what is an cohort effect and an example
The influence of membership in a particular cohort (past experiences may influence the outcome of data)
example -Tobacco use in the US…Fewer than 5% of population smoked around the early 1900s compared to WWW I/II era
War, famine economic, crisis experiences
Graduation class and curriculum emphasized during that time
what is an advantage of a cohort analysis
easier and less expensive to conduct than RCTs, the incidence (or rate) of exposure and outcomes can be estimated, and subjects in cohorts can be matched to limit the in
prospective
present to future timing of data collection
retrospective
past to present
historical prospective
the study of the impacts of efforts to control disease over time and the ways in which interventions have transformed patterns of disease and influenced disease transmission.
practical considerations in conducting a cohort study and the strengths and limitations
start with a group of subjects who lack a positive history of the outcome of interest and are at risk for the outcome
include at least two observational points - one to determine the exposure status and the second is to determine the number of incidence cases
advantages -Permit direct determination of risk.
Time sequencing of exposure and outcome.
Can study multiple outcomes.
Can study rare exposures.
disadvantages - takes a long time
Costly
Subjects lost to follow-up
types of follow up
active follow up - the investigators through direct contact with the cohort must obtain data on subsequent incident of outcomes
example
Minnesota Breast Cancer Family Study
1.Mailed survey
2.A reminder postcard 30 days later
3.A second survey
4/A telephone call to non-responders
passive follow up- does not require direct contact with cohort members
databases contained and maintained by organizations outside the investigation team
what is relative risk and how do you calculate it
is the ratio of incidence of disease in the exposed group to the incidence in the non exposed group
formula - incidence rate in the exposed/incidence rate in the non exposed
what is the best measure of association for cohort studies
relative risk
absolute measure - calculate the difference between the difference between the two measures
relative measure - calculate the ratio of the two measures of a disease frequency
what type of study is Framingham
cohort studies
examples of major cohort studies in the U.S
Nurses health study and physicians health study
odds ratio
1 applies no association
greater then 1 odds of disease/injury and disability due to exposure
less then 1 odds of disease /injury due to exposure
odds ratio - remember cross multiplication.
know the differences absolute and relative measures
absolute measures-provide a better idea of public health impact, i.e., the number of people affected.
example - an individuals height
relative measures -of association are commonly used in journal articles presenting research findings on etiology,
example -on a scale such as the yard or the meter
what is attribute risk and its formula
rate difference or risk difference
Calculating the EXCESS risk
Ie-INE
IE - incidence rate of diseases in exposed group
INE = incidence rate of disease in nonexposed group
external and internal validity
external validity - the study of who participate and how does it apply to the target audience
internal validity - is everything in the study done correctly
how is validity enhanced
- Chance - occurs by chance due to ph exposure
2.Bias -
3.cofounding - Truth
we must rule out 1-3 and then infer 4 through causal criteria
R - reliable
O - objective
A - accurate
R - reproable
know the difference between random and systematic errors and what contributes to random and what contributes to systematic
random error- un predictable changes introduced in the study.
factors that contribute to random error-
poor precision occurs
sampling error
variability in measurement
systematic error- errors in the design or implementation of a study, not random
factors that contribute to systematic error - Hawthorne effect, selection bias , information bias and cofounding
how can we increase precision
poor precision - occurs when the factor being measured is not measured sharply
consider the human factor , conduct routine maintenance
take multiple measurements
what is sampling error
occurs when the sample selected is not representative of the target 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
selection bias and how to reduce it among controls and cases
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.
how to reduce selection bias
-Develop an explicit (objective) case definition.
- Enroll all cases in a defined time and region.
- Strive for high participation rates.
- Take precautions to ensure representativeness.
what is information bias
information bias-Can be introduced as a result of measurement error in assessment of both exposure and disease
Recall bias: better recall among cases than among controls.
interviewer - 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
Differential completeness of medical records – occurs when cases and exposed subjects may have more medical records or more detailed records
how to reduce information bias
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 classification status
what is cofounding and how to control it
The distortion of the estimate of the effect of an exposure of interest because it is mixed with the effect of an extraneous factor
how to control it-
prevention strategies–attempt to control confounding through the Study Design itself and Analysis Phase
Three types of prevention strategies in the DESIGN PHASE:
1. Randomization
2. Restriction
3. Matching
what is publication bias
the failure to publish the results of a study on the basis of the direction or strength of the study findings.
know why we randomize: both advantages and disadvantages
why do we randomize - choose simple random sampling to make generalizations about a population
advantage -its simplicity and lack of bias.
disadvantage -difficulty gaining access to a list of a larger population, time, costs, and that bias can still occur under certain circumstances.
what is validity
improves data collection
how well the results among the study participants represent true findings among similar individuals outside the study.
which studies have a higher validity
when the participants and the situation studied are similar to those that the researchers want to generalize to and participants encounter every day.
studies that are classified as level 1 have the highest number of validity
clinical trail history examples
In 1537 Ambrose pare applied to experimental treatment for battlefield wounds
east Inidia shipping company 1600 - found that lemon juice protected against scurvy
james lind (1747 ) used the concurrently treated control group method
Characteristics of clinical trails and examples
clinical trials - a planned experiment outcomes in treated groups are compared with outcomes in the experiment control group same time period
examples -
medical Research Council Vitamin Study—studied role of folic acid in preventing neural tube defects.
South Bronx, NY, STD Program—evaluated effectiveness of education efforts to prevent spread of sexually transmitted diseases (STDs).
Women’s Health Initiative – elevated risk for breast cancer and CVDs after Hormone Replacement Therapy (HRT)
single blinding vs .double blind design
single blind design - subject unaware of group assignment the researcher knows
double blind design - neither subject nor experimenter is aware of the group assignment
phases of trail and the purpose of each phase
phases of clinical trail -Before a vaccine, drug, or treatment can be licensed for general use, it must go through several stages of development
phase 1 -tests a new vaccine in adult volunteers (fewer than 100 volunteers).
purpose: doctors learn about the learn if a new drug, treatment, or treatment combination is safe for people. They may have already tested it in laboratory animals. and side effects.
phase 2 -expands testing to a group of 100 to 200 subjects (from the targeted population).testing out the safety measures in a large group population
purpose :safety, effectiveness, specificity. how well it works
phase 3 the main tests -assesses the efficacy of the vaccine in the target population. compare the rate of infection and placebo groups
purpose: confirm does it work in a larger population target audience ,monitor safety
phase 4-Tested for effectiveness in the general public
purpose : how well does it work in a general population. efficacy
examples of randomization purpose ,advantage and limitations
purpose - helps prevent bias since it occurs when a trail results are affected by human choices or other factors not related to the treatment being tested
advantage- it eliminates selection bias
balances the group with respect to many known and unknown confounding factors
disadvantages -
Power calculation might demand vast samples size, which require more resources from the investigators.
Validity requires multiple sites, which will be difficult to manage.
common clinical trail designs
two arm RCT - placebo vs treatment
cross over RCT - placebo vs treatment- measures outcomes, washout period then switch and measure outcomes
factorial RCT design -when more then one treatment is applied to answer more than one question( less common)
what is ethnics with regards to human subjects protection
informed consent
respect of persons, beneficence and justice.
Competent investigators and good research design lead to a greater likelihood of benefits, protect subjects from harm, and ensure that peoples’ time is not wasted and their desire to participate in a meaningful activity is not frustrated.
strengths and limitations of clinical trails
strengths of clinical trails -
They provide the best means of minimizing the effect of confounding.
They avoid bias in allocation to exposure groups.
Large randomized clinical trials are the best design for detecting small to moderate effects that may be clinically important.
limitations -Ethical issues need to be considered.
They are usually time consuming and costly.
strength and limitations of community trials
unit of analysis - group or community
control - sometimes
randomization - rare like flipping a gold coin
strengths -
patients do not have to travel far to participate in a clinical trial, which can boost enrollment and advance scientific knowledge.
smaller independent practices
limitation - fewer study units are capable of being randomized which affects comparability
affected by population dynamics ,secular trends and nonintervention influences
examples of community trails
In the 1940s the effectiveness of fluoride in preventing dental caries was tested comparing the frequency of caries in the children in Kingston and Newburgh.
Stanford three community trail
Hawthorne effect
the alternation of behavior by the subjects of a study due to their awareness of being observed
people are working harder when they are being watched and you can hide the participants
if the study is retrospective looking at conditions in the past at a single point or range of time what should be used
odds ratio
if the study is prospective treatments under the control of the researcher over a period of time what is usually preferred
relative risk
“Self- reported injuries among left-handed and right- handed people were compared in a survey of 1,896 college students in British Columbia, Canada. Lefthanders were more likely to report having had an injury requiring medical attention during the last two years (OR=1.89, 95% CI 1.39, 2.58). The odds was highest for lefthanded males when driving motor vehicles (OR=2.35, 95% CI 1.25, 4.43). Regardless of handedness, males had slightly higher odds of injury than females.”
case control study
“The authors examined the cross-national correlation of alcohol consumption (based on food availability data) and breast cancer in 20 developed countries. Weighted correlation coefficients for alcohol and breast cancer were 0.31 for mortality and 0.65 for incidence; the corresponding unweighted coefficients were 0.50 and 0.45. Correlation coefficients for fat consumption and breast cancer ranged from 0.69-0.89. After adjustment for fat consumption in multiple regression models, the positive alcohol-breast cancer association disappeared, while the fat-breast cancer correlation remained positive and strong. These findings do not support the positive alcohol-breast cancer association that has been suggested by analytical epidemiological studies. The multivariate results, however, should be interpreted with caution due to the potential variation in the extent to which national alcohol data reflect consumption among females.
ecological study
In a classic study in the investigation of the health effects of cigarette smoking, volunteers working in 1,121 counties in 25 states in the U.S. recruited 447,196 men, age 33-92 and had them complete a questionnaire about their smoking habit. Five years later, 39,178 of these men had died, and it was concluded that life expectancy was diminished by cigarette smoking. Which of the following best describes the design of this study?
prospective cohort study
Questionnaires were mailed to every 10th person listed in the city telephone directory. Each person was asked to list age, sex, smoking habits, and respiratory symptoms during the preceding seven days. About 20% of the questionnaires were completed and returned. About 10% of respondents reported having upper respiratory symptoms
cross sectional study
Records from 1,500 employees of a major aircraft company in 1951 were reviewed. These records were then classified by diagnostic criteria for coronary artery disease (CAD). New cases of CAD have been identified by examinations every three years and through death certificates until the present day. Relative Risks have been computed.
retrospective cohort study
A random sample of middle-aged sedentary adults were selected from four census tracts, and each person was examined for coronary artery disease (CAD). All persons without disease were randomly assigned to either a two-year program of aerobic exercise or a two-year arthritis-prevention non-aerobic exercise program. Both groups were observed semiannually for incidence of CAD.
randomized control study experimental study
A 39-year old woman presents with a mild sore throat, fever, malaise and headache and is treated with penicillin, for presumed streptococcal infection. She returns in a week with hypertension, fever, rash and abdominal pain. She responds favorably to chloramphenicol, after a diagnosis of Rocky Mountain spotted fever is made.
case study
500 people exposed to recent radiation exposure were recruited and followed for the next 30 years to measure cancer incidence
prospective cohort
Patients admitted for carcinoma of the stomach and patients without a diagnosis of cancer are interviewed about their chewing tobacco history to assess the possible association of chewing tobacco and gastric cancer.
case control study
Data on median income for households in census tracts within a large metropolitan county in the U.S. were obtained from the Census Bureau’s Current Population Survey. Air pollution levels were measured in these same census tracts during a period of one-month. The data were analyzed using a geographic information system (GIS) to produce maps showing pollution and income levels by census trac
ecologic study
Ethical issues aside, which one of these studies could provide the strongest evidence that formula feeding increases risk of DM?
study D is the strongest Send letters and make follow-up telephone calls to 1,000 mothers of newborn babies asking the mothers to participate in a study in which the investigators will randomly assign mothers to breastfeed or formula feed and will review the annual pediatric visit records for the child through age 20 years.
study C is an alternative if you can’t do study D
Send letters and make follow-up telephone calls to the mothers of 1,000 12-year old boys and girls who have tested negative for diabetes within the past six months. Request the parents’ consent to review their child’s medical records annually until the child reaches age 20. Obtain information on infant feeding status from the medical record and a parental questionnaire.
Which one of these studies would be the most problematic for inferring the existence of an association between infant feeding practices and subsequent DM at the individual level
study E
Examine the correlation between per capita formula sales and DM prevalence across the 20 towns in Maramba.
Which one of these studies would provide data that can be used to estimate the prevalence of DM at the time of the stud
Review pediatricians’ records to select a random sample of 1,000 youth age 12-19 years old to send out a survey to record DM status and infant feeding history from each youth.
Which one of the observational (i.e., non-experimental) studies would provide data to estimate the incidence of diabetes in breastfed children?
Send letters and make follow-up telephone calls to the mothers of 1,000 12-year old boys and girls who have tested negative for diabetes within the past six months. Request the parents’ consent to review their child’s medical records annually until the child reaches age 20. Obtain information on infant feeding status from the medical record and a parental questionnaire.
Study C
Assuming that the exposure data are accurate, how significant a concern would inability to establish temporality (time sequence of exposure and outcome) be in Study C?
There is high concern because without this you cannot conduct study C appropriately
