# Questions tagged [epidemiology]

Epidemiology is the study of the distribution and spread of disease or illness at the population level.

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13 views

### What is the unity of biostatistics with epidemiology?

It occurred to me that the distinction between biostatics and epidemiology is maybe converging in this new era of big data analytics. I seek insight into the unity of statistics with epidemiology; ...
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### is it possible for odds ratios' or risk ratios' confidence interval to contain 1 and still be statistically significant?

my understanding is that if a 95% CI for odds ratios and risk ratios contains 1 then it is not statistically significant. However I have seen in studies such as https://pubmed.ncbi.nlm.nih.gov/...
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### How to use poisson to predict incidence rates per 100,000?

I am trying to make predictions with a poission model to get the predicted incidence rate per 100,000 of some event. My problem is that when I compare the predicted incidence to the incidence ...
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### To include or not the event indicator in modeling probability of treatment censoring

Setup In observational studies, inverse probability of censoring weights (IPCW) can be used to adjust for informative loss to follow-up or in the context of non-compliance, treatment switching. I'm ...
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### Sample size calculation and 95% CI for incidence rate

I need to calculate the necessary sample size for calculating the incidence rate of severe infections in an at-risk population. Also wish to know the best method to calculate 95% CIs. As an example, ...
1 vote
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### Sample size calculation for a difference between two groups with clustered data

I want to compare proportions or means in two groups in a clustered sample. Suppose the sampled clusters are schools or hospitals or Census areas, and we sample from each of these an equal number in ...
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### Log of a log-transformed variable

I have been suggested to use the log of a log-transformed independent variable (i.e., log(log healthcare expenditure)). I am not sure how would this make sense. Is this a standard practice (in the ...
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### How to convert continuous relative risks per exposure unit?

If a study for example concludes that the relative risk of a cardiovascular event is 1.04 per 10 µg/m³ increase in NO2, how can I calculate the relative risk for an air pollution concentration of for ...
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### Interpreting the fitted model outputs from a covariate-adjusted ROC curve in the AROC package

Below I have fitted a covariate-adjusted ROC curve (AROC) using a semiparametric Bayesian normal linear regression model available in the R package “AROC”. However, I am not clear on how to interpret/...
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### Comparing Proportions Grouped by State of Residence

I am looking at whether one racial group has disproportionately low rates of a medical procedure compared to the racial makeup of their state - across all 50 states. My dataset has the state the ...
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### How to compute marginal hazard rate from parametric survival models?

Suppose that the conditional hazard rate for subject $i$ follows a proportional hazard model in the form of: $h_i(t)=h_0(t) exp(\beta_1X_{i1}+\beta_2X_{i2}+\beta_3X_{i3})$ $X_i$ are subject-specific ...
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### Age and sex standardised incidence rates

If I were to compute age-sex standardised incidence rates based on a simple random sample of a nationwide household survey on hearing loss. Noting that this a sample not the total population, so the ...
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### Determination of sample size in multi-center trials

I was the reading the Bland's chapter about sample size determination, and in the last part he talks about "Trials randomized in clusters" (ie. 50 patients of 30 GP physicians where each GP ...
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### Assumption of Poisson regression with robust standard errors

I am applying a Poisson regression with robust standard errors to model a binary response variables. I was wondering what are the assumptions underlying this type of regression? I understand that the ...
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### Lin’s concordance correlation coefficient is low but numbers are close. Any reasons?

I am working out Lin’s concordance correlation coefficient (CCC) for incidence and prevalence between two methods for different diseases. For most of my comparisons i get a high CCC of arouynd 0.95. ...
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### Cleaning up several crude odds ratios from several sources

Does anyone know a formula for pooling odds ratios across studies? I'm trying to do a quick pen and paper pooling of different numbers of odds ratios from different studies where I don't have the ...
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### Sampling weights in Cox proportional hazards models

I'd like to use sampling weights in a Cox proportional hazards regression model to address selection due to different response probabilities. I'm calculating the weights as Inverse Probability of ...
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1 vote
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### How to estimate disease prevalence using logistic regression when some people are measured several times

I have a binary variable indicating the presence or absence of a disease as well as variables for time and other covariates. SOME (not all) people are observed (tested) several times. Suppose I want ...
1 vote
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### How to check confounding and mediation in large dataset?

Given a large dataset, one cannot possibly check every model. In particular, it does not seem clear to me that one can check confounding or mediation in either cases. How does one check confounding/...
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### Analysis on repeated measurements with only one follow-up outcome

I would like to analyze the association between dietary intake and a specific health outcome. Now suppose I have 100 subjects, each having 10 repeated measurements of dietary intake collected from the ...
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### How to prove change in a time series when the population is growing?

I have a small dataset with data on the number of heart and liver donors from deceased patients each year (from 2012 to 2021). I would like to find out if there has been a change in the number of ...
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### Probability that seems to exceed 1

Suppose we have the following information based on independent events: The probability of contracting Alpha variant is .4 The Delta variant is 50% more contagious than Alpha The Omicron BA1 variant ...
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### Will threshold of logistic regression change accuracy? Any relationship with the incidence of disease? [duplicate]

I am using a logistic regression model to predict breast cancer. I trained and tested the model in a population with a pretty high incidence of breast cancer(since the individuals all went to the ...
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### Some help on this question about stochastic epidemic models without removals would be greatly appreciated

I get this question up until the underlined part, would someone be able to explain the rest of it to me as its had me stumped for a little while now.
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### Targeted Learning in Data Science: background material

I am interested in the use of modern causal inference methods to research the association between a (non-genetic) exposure, and endogenous molecules and/or health outcomes (high-dimensional data). I ...
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### Disease Control Rate for a Clinical Trial problem

Recently, I have come across a 2-armed clinical trial problem which attempts to find a "Disease Control Rate" (DCR) for patients in the treatement and placebo arms. On the Internet I found ...
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### Multiple associations in Relative Risk and Odds Ratio

I am a frequent user of the package (epiR), especially in Relative Risk and Odds Ratio. Generally, I use several covariates to make the associations (RR or OR), for example: outcome (death) versus ...
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### Should you include time as a continuous predictor when estimating incidence or prevalence?

Suppose one has a time series of disease counts and populations (at risk, total etc.) or, equivalently, binary events of disease status. Then suppose one wanted to present estimates of incidence or ...
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### What to do if there are not enough controls per case?

I conduct a case-control study (matching by age) where I have a ratio of 1:2, i.e., 2 controls per case. However, this ratio is not sufficient for all cases. Example: If I have 30 cases with 70 years, ...
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### How to interpret this formula with probability of an individual becoming infected over x days?

I am trying to understand a formula in this paper (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5444538/#:~:text=Low%20Risk%20of%20International%20Zika,the%202016%20Olympics%20in%20Brazil). In the ...
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### What is the covariance between two log relative risks?

In a randomized experiment with two groups (treatment and control), suppose the response variable, $Y$, has 3 categories (0,1,2): $y_{0_{i}}$,$y_{1i}$ and $y_{2i}$, in which $i$ denotes the $i^{th}$ ...
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### Calibration of an agent based epidemic model on an HPC

I am working on HIV modeling with the EpiModel R package and we are trying to smooth our calibration process by efficiently using the Slurm clusters we have available. For reference, this is one of ...
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### prevalence ratio question

I understand that prevalence ratio is ...
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### Averaging time-dependent, heteroscedastic estimates of vaccine efficacy over time periods

Vaccine efficacy against Omicron has to be estimated for three months since the second dose. Efficacy data are given for shorter periods comprising three months. For example, the table, based on Fig ...
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### What is the relevance of comparing the number of positive Covid cases at the same date in 2020 and 2021?

I am following the news in a country (which I will leave unnamed) where I am currently on holiday. Same as in a related question I asked last year, I find myself completely baffled and dumbfounded by ...
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### HOW to determine $S$ in $SEIR$ epidemiology model

With the contact rate parameters for a $SEIR$ model as follows:  \begin{aligned} \beta &= 0.139\\ \gamma &= \frac{1}{10.4}\\ \sigma &= 0.1\\ R_0 &= 1.4456\\ N &= 3,787,000\\ I(0) ...
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### How well do Covid-19 forecasts work?

I hope this question is in the scope of CrossValidated (I think so because it is in the end about statistical analyses and machine learning, I am not looking for individual opinions but for reviews or ...
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### Help Requested - Bayes' Theorem posterior odds > 1 when applied to covid test

I took an antigen test yesterday and was trying to create a tool to help me interpret the results via Bayes' Theorem. I used actual sensitivity and specificity numbers from the CDC, calculated odds of ...
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### How trustworthy are biomarker estimates and conclusions in this covid vaccine paper?

My question is about the Correlates of protection against symptomatic and asymptomatic SARS-CoV-2 infection paper from the developers of the ChAdOx1/Vaxzevria vaccine. The paper establishes ...
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### Modeling Case Fatality Rate (CFR) outcome variable in cross-sectional study using GLM

Background I am conducting an analysis examining the association between various predictors on COVID-19 Case Fatality Rate (CFR), which is defined as the proportion of mortality among confirmed cases ...
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### Time varying effect in time dependent cox model

In the case of Stanford heart transplant dataset (jasa), is it possible to check if the effect of the time dependent covariate of transplant is time varying as well ? If that's the case can we compute ...
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### Time after time-dependent variable in Cox model

I am trying to create a time dependent (covariate) cox regression model for a survival analysis project I am interested in. A brief overview of my dataset: I have a cohort starting from 2011-01-01, ...
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### Misclassification: differential and non-differential random and systematic

How to identify if misclassification is differential and non-differential?? Also need help distinguishing between: Differential random Differential systematic Non-differential random Non-differential ...
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### Types of misclassification bias

Would someone please be able to give an explanation of when the following misclassification biases would occur? I am completely lost! Non-differential random Non-differential systematic Differential ...
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### Calculation of 95% Confidence Interval for an Incidence Rate Difference

Suppose that I have two pre-computed Incidence Rates with 95% CI, calculated from the same sample. Let's say IR1: 10.0% [8.0-12.0%] IR2: 21.0% [15.0-27.0%]. If I want to calculate an IR difference, ...
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### Interpretation of the E-value for non-epidemiologists

A recent method for sensitivity analysis is the E-value (VanderWeele and Ping, 2017). Yet, I'm still struggling with the interpretation of such a value. Coming from outside of epidemiology, where risk ...
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### Calculating patient-years from average follow-up

I need to estimate patient-years for some studies, in which this data is not reported. However, I do have total population and mean follow-up. Would it be suitable to estimate the number of patient-...
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### Retrospective cohort study and case control study

What study would best suit looking at the association between low birthweight and later academic performance? Note - 1000 low birth weight children and 3000 normal birthweight children were included ...
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