Epidemiology is the study of the distribution and spread of disease or illness at the population level.
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What is the definition of “source population”?
What is the definition of source population?
Suppose we screen $100,000$ people and then include $50,000$ people in three studies $A$, $B$ and $C$. For study $A$, is the source population the ...
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1answer
85 views
How to interpret odds ratio?
Suppose we have a baseline exposure group and 2 other exposure groups for a case control study. Suppose the odds ratio for the first exposure is $1.5$ and the odds ratio for the second exposure is ...
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1answer
27 views
Confounding variables
Suppose we want to study the association between alcohol consumption and cancer. If we include people who also smoke (a confounder), would this lower the relative risk of cancer for alcohol drinkers? ...
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44 views
Can GEE handle small unaccounted clusters in data?
A survey is being administered in a resource intensive setting. A 2-phase study design will be implemented using cases and controls identified by a certain behavior (say, smoking) and they will be ...
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2answers
105 views
How do I calculate whether something is an independent risk factor?
I do not know what calculation/formula to use to show that something is an independent risk factor.
E.g., in a cohort study:
Group A (n=1000) - exposure to X - outcome exposed 70/1000 demonstrate Z
...
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43 views
Computing event rates given RR + CI and total sample size in each treatment group
I am looking at some data for the risk of mortality in patients undergoing treatment A vs treatment B and I am given the total number of patients in each treatment arm and the relative risk + ...
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1answer
56 views
Conditional fixed effects Poisson *with population exposure*
Reading a paper, the authors use a "Conditional fixed effects Poisson with population exposure." I wasn't sure what "population exposure" meant, so I looked it up. It seems like the term comes from ...
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2answers
87 views
Ways to Estimate Date of Conception
Why don't epidemiologists ask people when they had sex? Why do they estimate time of conception from the birth date? This seems to introduce unnecessary error. Wouldn't it be better to record the time ...
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45 views
Calculating confidence intervals for prevalence differences
I would like to calculate the confidence intervals for prevalence differences. If I have the CIs for the prevalence, can I simply subtract the upper limit of one Ci from the upper limit of the other, ...
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1answer
50 views
Simulation of woman's age of getting breast cancer (cumulative incidence rate)
I am writing a programme to simulate the age at which women will get breast cancer. I have data on the cumulative incidence rate for the whole population.
What I am doing right now is using Monte ...
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2answers
62 views
Is it fair to say that most epidemiological studies are observational?
Is it fair to say that observational studies are the 'bread and butter' of epidemiological studies?
By epidemiological studies I mean studies looking for an association between an environmental ...
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0answers
89 views
Collapsibility: Odds Ratios versus Risk Ratios
It is known that odds ratios enjoy a certain symmetry. For example, the odds ratio of outcome $Y$ is the inverse of the odds ratio of outcome $\neg Y$. Risk ratios, on the other hand, do not enjoy ...
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1answer
73 views
Incidence density
Suppose there are $6$ people in a population. During $2$ weeks $3$ people get the flu. Cases of the flu last $2$ days. Also people will get the flu only once during this period. What is the incidence ...
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1answer
364 views
Power calculations, logistic regression with continuous exposure--cohort
I'm trying to estimate power in a logistic regression with a continuous exposure in a cohort study (ie, the ratio of the sampling probabilities is 1). I have population cumulative incidence ...
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2answers
152 views
Estimator for an incidence rate
While going through a statistics course for medicine students, I ran accross a problem related to incidence rates. The context of the problem is a chapter about the Poisson distribution. In the ...
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0answers
45 views
Dealing with dependant data when estimating probability of an event happening
I have 10 year worth of data from 1970 to 1980 (40 quarters).
For each quarter I have five measurements M1, M2, M3, M4 and M5.
TWIST: Although the data I have is on individual patient level the ...
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0answers
104 views
What should this poor guy be told? [duplicate]
Possible Duplicate:
What are the chances my wife has lupus?
A day or two ago a man posted a question on math.stackexchenge about whether his wife likely has lupus, given the diagnosis. ...
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2answers
120 views
Basic reproduction number
I'm not sure where to post this, so I thought I'd post it here. If there is another better place to ask this question then please could you let me know.
Let
$\beta$ = rate of infection, and ...
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2answers
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PCA- does KMO need to be over 0.5?
I'm doing principal component analysis (PCA) on my nutrition data. Basically, I want to condense 43 food groups into fewer groups (aka, I want to define 2-3 patterns based on the 43 food groups). The ...
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Can I validly expand the odds ratio analogously to the relationship between relative risk & the incidence rate ratio?
I am involved in a nested Case-Control study that involves cohorts of cases and controls entering a program, with the outcome of failure by six months. Cases and controls are individually matched on ...
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2answers
173 views
Looking for ways to compare between coxph models
I'm running Cox proportional hazards regression in R, and would like to test the option of categorizing one of my continuous variables to factor (I'm aware of the loss of data issue, just checking).
...
9
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1answer
169 views
How to deal with death in disease-free survival analysis?
If I have disease free survival data (defined as whether or not a particular disease has been diagnosed or not along with the time to that event or loss to follow up) and also overall survival data, ...
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2answers
180 views
Terminology for different types of epidemiological variable
If I have a data set with $n$ patients and I have a categorical variable $X$ for each patient, I want to drop all patients whose $x$ is a particular value.
Question 1: what is the term (preferably ...
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3answers
922 views
Comparing incidence rates
I want to compare to incidence rate's between two groups (one without a disease and one with).
I was planning to calculate the incidence rate ratio (IRR), i.e. incidence rate group B/ incidence rate ...
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2answers
346 views
T test and P value [duplicate]
Possible Duplicate:
What is the meaning of p values and t values in statistical tests?
I currently start epidemiology class, I am very confuse of p value and t test, what do they mean? how ...
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1answer
182 views
Post-hoc analysis for Logrank test
I need to perform survival analysis for 4 different groups in a study. When I use the Logrank test, the null hypothesis is rejected.
My question is, how can I tell now exactly which pair of groups ...
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25 views
Resources for modelling diffusion of service adoption/churn
I'm looking for existing models and try to design my own to predict the spread of service among connected people (real social network).
So far I have tried game theory and some epidemic models but ...
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1answer
528 views
Estimating misclassification rate from summary classification values
I'm trying to work out the misclassification rate in a published study, where the results do not include this value. However, I have the sensitivity, ...
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3answers
408 views
More interpretable measure of association than odds ratios for contingency tables with 0 counts
How strong/weak of a correlation is this?
...
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1answer
142 views
Survival analysis for nested, censored and dependent data
I have to analyse the effects of different treatments on the survival of individuals for 1 week.
But:
the data are 'grouped': individuals were grouped by 10, and the survival probability is ...
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2answers
874 views
What is the conventional definition of recurrence-free survival?
Hello to all the biostatisticians and epidemiologists out there,
I have looked up and down for a standard definition of recurrence-free survival, and the issue I'm having is determining if the ...
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1answer
184 views
Follow-up updates in case-cohort designs
In a case cohort, you randomly sub-sample some feasible number of the cohort (say 20%) and then afterwards add all of the cases that were not part of the sub-sampling. So while a case-cohort is easy ...
5
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1answer
148 views
Imputation of a censored variable
I have a medical dataset with approx 200 variables. One of the variables is a bio-marker (concentration of a particular enzyme). It's distribution is right skew, and the problem is that values above a ...
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3answers
160 views
What to conclude when you fail to find an association in an epidemiological study?
Normally when somebody finds an association in an epidemiological study people are quick to point out that it doesn't prove causality, that there are problems of missing co-founders, that it is at ...
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1answer
133 views
Using mle2() for age-period-cohort models
I've followed guidelines for comparing models in Chapter 6 of Bolker's Ecological Models and Data in R, applying code used in this section to cancer count data. The models include parameters for age ...
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0answers
177 views
How to test the equivalence of clinical parameters between two contingency tables (confusion matrix)?
What will be the easiest way to compare the derivations (clinical parameters) from two contingency tables? I want to test two 2x2 tables with their respective True Positive, True Negative, False ...
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57 views
Inferential methods on large panel data with sparse clusters and rare outcomes
Using longitudinal survey data on children using psychotropic medications, we are interested in estimating associations with medication classes, their persistence and adherence (longitudinal ...
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0answers
55 views
How to test the effect of intervention on patients quality of life?
I am carrying out an evaluation for an intervention using secondary data. Unfortunately the design of the study is weak as participants cannot be randomised. I am looking to see whether the ...
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1answer
333 views
Sample size calculation for truncated normal distribution
So, I am new here.
I need to perform a sample size calculation for a clinical trial. The study sample will be select according to criteria of person's height. Persons within the particular height ...
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0answers
115 views
How to implement a two-stage hierarchical model of time series data in R?
I'm currently working with a data set that consists of a monthly case count for several sites, along with a number of site-specific covariates. We're trying to estimate the effect of one of them on ...
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0answers
90 views
How should I model a Dose-Response Curve with Resistant Subpopulation?
I am looking at the relationship between an environmental exposure and a health outcome. Measurements have been taken on subjects at a number of different time points and I am trying to work out if ...
6
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2answers
419 views
Use of propensity score in a case-control study
The theory of propensity score (PS) suggests that it should only be used for the cohort study because PS matches the "treated/exposed" to the "un-treated/un-exposed" groups. However, cases and ...
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0answers
299 views
Measure score change over time while accounting for baseline differences
I'd like to test for and estimate group differences in NIHSS (National Institute of Health Stroke Scale) change between hospital discharge and three months after hospital discharge.
Because the score ...
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0answers
81 views
Bayesian plots: construction and interpretation
I've heard a couple of definitions of a Bayesian plot, but I am not 100% sure what it is and whether it is possible to plot this in an R.
An example of the plot is here: ...
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0answers
60 views
Breast Cancer Screening [closed]
I have a couple of questions about screening:
Does breast cancer screening change the incidence of breast cancer?
I think that it does not since screening is not a diagnostic tool. Also it is ...
3
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2answers
121 views
Calculating risk of disease
Suppose we are doing a cross sectional study on heart disease in males and females. If $16/10000$ males have heart disease and $10/10000$ females have heart disease, can we conclude that men have a ...
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1answer
59 views
Cost Benefit/Effectiveness
I would like to compare the results of several diagnostic modalities on a population to identify a disease. More specifically I would like to compare the sensitivity of the modalities (all have 100% ...
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0answers
54 views
Pre-process classification data according to ‘amount of evidence’
I have an area which is divided into polygons of different sizes. Each polygon has the same associated features/predictors and I know whether something occurs within the polygon or not. If something ...
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1answer
112 views
How to compute confidence interval for number to treat in a logistic regression?
I have built a multivariate regression model where $\mathbf x$ is the variable vector. Now I am asked to calculate the confidence interval for the number to treat (NNT) at $\mathbf x=\mathbf {x_0}$ ...
