Questions tagged [epidemiology]

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

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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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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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80 views

Error models for COVID-19 prevalence data

1) Some background I'm currently learning about compartmental ODE modeling for epidemiology (inspired by the current pandemic!) and I've been exploring parameter estimation of SIR-like models using ...
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Why can't we reliably compare states?

I came across this catchy visualization on reddit showing the percentage of adults reporting binge or heavy drinking in the US: https://www.reddit.com/r/dataisbeautiful/comments/nve04b/...
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Understanding a simple post-hoc power analysis of effect size

I am trying to understand a relatively straightforward paragraph found in "Gun Shows and Gun Violence: Fatally Flawed Study Yields Misleading Results" by Wintermute et al that appeared in ...
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How to implement this two-stage regression model (nutrition research)

The textbook Modern Epidemiology 3rd edition (pages 435-437) introduces a very interesting hierarchical model for studying the effect of food consumption on disease. The typical model for studying the ...
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Multimodal SIR model

I am trying to model covid 19 infected number of cases, given current data in my region, the number of infected people is a graph with 3 peaks, is it possible for an SIR model to incorporate this? I ...
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120 views

How can we distinguish the effects of a lockdown from those of a vaccine?

My question is related to Covid-19 specifically, but it can be generalized to any infectious disease. I am asking this since I am reading a lot of information on several Social Media regarding one ...
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1answer
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"Have you ever …" as a question for measuring cumulative incidence

In Gordis Epidemiology, it is stated that the interview question Have you ever had asthma? can be used to measure cumulative incidence. Cumulative incidence was ...
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calculating odds ratio confidence intervals

I have a question about the formulas for confidence intervals for odds & odds ratios. In a nutshell I understand the logic behind the formula for the odds confidence interval, but the same logic ...
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SIR: parameter estimation and optimization here (R)

From here https://ourworldindata.org/coronavirus/country/israel I have extracted the Covid Data for Israel, with some manipulations, I have obtained the plot of the daily new infections in Israel If I ...
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To match or not to match when 2 exposures are inextricably confounded with other variables?

I want to study the effect of two Groups of patients ($X_1$) on $y$ (a test performance score), in a GLM framework. Age ($X_2$) and Education ($X_3$) are potential confounders on $y$. However its not ...
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How can mortality rate of a cohort population be converted to a +/- number of months or years from average life expectancy?

How can mortality rate of a cohort population (eg: 65/1000 annually for those who smoke 1 pack per day) be converted to a plus or minus number of months or years from average life expectancy, as seen ...
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How to calculate proportion of the population

I am trying to calculate population attributable fraction. The formula that i am using is $$ \frac{P_e(RR-1)}{P_e(RR-1) + 1} $$ I am using this website as guide: https://sphweb.bumc.bu.edu/otlt/mph-...
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Estimating future graph size given partial graph size

(This question compares a branching-fiction novel to a disease, bear with me.) This is for fun, my friends and I are writing a branching-fiction novel: A black node is a concluding chapter ("The ...
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Why are most epidemic models continuous-time?

Most classical epidemic models such as SIR and variants are formulated as differential equations. However, to me discrete-time models feel more natural to measure the evolution of a disease on a day-...
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How and why do epidemiology and econometrics models handle multi-collinearity differently?

Linear multiple-regression models are often built differently according to discipline. In epidemiology, a linear multiple-regression may be fit to test associations using hypotheses about model ...
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1answer
66 views

How is the vaccine effect calculated?

I'm trying to understand this study about the vaccine effect for the COVID. In the results the authors state: We found that VEs increased over time until a peak at day 28-34 days post-vaccination for ...
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Ignoring random effects when few data points are correlated

Suppose we have covariates $X_{ij}$ and responses $Y_{ij}$ where there is correlation in the response with the same $i$. This amounts to the data being correctly modelled by a mixed effects models, ...
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Do health departments inform hospitals/clinics of disease trends?

For example, during a common cold epidemic, do doctors get reported beforehand that there is a trend going on so that they can use this information to suspect diagnosis? Does every health care unit ...
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How to estimate the change of rate of COVID-19 infections when accounting for vaccine effectiveness and increased transmissibility of mutated strains?

The world has reasonably accurate numbers of the transmissibility of the strains of COVID-19 that have ravaged humankind. Now, two changes are afoot: Some wealthy regions have access to limited ...
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How to determine "per" population size for incidence rate

I am reading notes for a given assignment and incidence rate is defined as $$ \frac{new cases}{observed population} x 10^n $$ The only thing that is confusing me is that what to use for ...
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61 views

Fitting SIR model for COVID-19 Data UK

I want to fit a COVID-19 SIR model for UK to evaluate the lockdown measures (here: the first lockdown). My code is based on https://kingaa.github.io/clim-dis/parest/parest.html#overdispersion-a-...
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Why do we measure incidence, if we can measure the prevalence of a disease for two successive years instead?

Why do we measure incidence, if we can measure the prevalence of a disease for two successive years and then subtract the latter year's figure from the former years number and find out the incidence? ...
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How to estimate prevalence with a zero incidence (rare disease)? [duplicate]

I had to solve the following problem. Newborn screening has been implemented for a very rare pathology. For 6 months, and out of 50,000 births observed, no sick case was observed. What is the ...
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Is it ok to use volunteers for prospective cohort studies

Prospective cohorts are ones where the exposure is known but not the disease outcome. Volunteer bias is where volunteers tend to be healthier. I've been told because of this volunteer bias, we should ...
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32 views

Estimate recovered/infectious for SIR model

I like to fit a SIR model to COVID-19 data of UK. If i understood it correctly i need the numbers of I (infected) people (and not the reported case daily case data) which i would calculate as followed:...
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34 views

How do I incorporate clustering in a matched case-control analysis?

I am trying to analyze a 3:1 matched case control study (matched on age and date of medical encounter) but realized that there may be household clusters represented among cases and controls. Cases ...
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45 views

Calculating significance on incidence rates

This is my first time attempting a project like this so my question might be quite wordy. I am analysing the trends in incidence of disease X on the population over 30 years. I have grouped the 30 ...
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A new strain of covid-19 is 70% more infectious/transmissible. What does that mean and how has it been estimated/measured? [closed]

70% in the media https://www.dailymail.co.uk/news/article-9070683 Prime Minister Boris Johnson told a Downing Street briefing that early analysis showed the new strain could increase the reproductive ...
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636 views

Why is $R_t$ (or $R_0$) and not doubling rate or time the go-to metric for measuring Covid-19 expansion?

In my head, the natural way to measure the expansion speed of an epidemic across populations of different sizes is simply fitting an exponential over recent infection numbers (with any strategy), ...
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Questions about distributed lag non-linear models (DLNM)

I am new to DLNM, I have some confused questions: My research is about the environmental impact on health, and my data records are ordered as health cases as below: I want to use DLNM to analyze the ...
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Why not always present logistic regression estimates in the response scale (probablity)?

There's a lot of discussion in epidemiology around the relative merits of odds ratios vs risk ratios. Proponents of the former cite the mathematical qualities of odds (not constrained to be between 0 ...
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from x per 100 person-years to x per 100,000 person-years?

If something is reported in per 100 person-years, like in the below table, is it possible for me to convert it into per 100,000 person-years simply by multiplying by 1,000? That is, 2.21 per 100 ...
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Which statistical model is being used in the Pfizer study design for vaccine efficacy?

I know there's a similar question here: How to calculate 95% CI of vaccine with 90% efficacy? but it doesn't have an answer, at the moment. Also, my question is different: the other question asks how ...
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How to calculate 95% CI of vaccine with 90% efficacy?

A vaccine is reported in the news to have 90% efficacy. I'd like to know how much confidence there is in that efficacy measure. The protocol for this reports that a vaccine or placebo was administered ...
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1answer
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looking for the probability of infection (for Covid19) vs the number of days to the onset of symptoms

I have been searching for a graph of the probability of infection (for covid 19) vs the number of days to the onset of symptoms. The following graph is taken from Namilae, et al (Multiscale model for ...
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Why do some researchers use the oxymoron "prevalence rate"?

An incidence rate (whether an incidence density or an incidence proportion) measures the probability of an event (typically a new case of the relevant health condition in epidemiology) divided by time....
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Estimating True COVID-19 infection rate from Positivity Rate?

Like many, I've been watching and tinkering with COVID-19 statistics for the past 8+ months. One thought I keep coming back to is that there must be some smart Bayesian approach to blending (a) known ...
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Best way to infer number of infected from number of new cases per day

Lots of the covid-19 datasets (e.g. https://ourworldindata.org/coronavirus) only provide the new cases per day data. However to fit a model such as e.g. SIR to this ...
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1answer
144 views

Calculating risk difference and number needed to treat from hazard ratio in meta-analysis

If you have primary data, there exist several ways to calculate a risk difference (RD) or number needed to treat (NNT) from time-to-event data (see e.g. following pmid: 29955580, 31626655). However, I ...
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1answer
33 views

How to do propensity score matching for a cohort study?

Suppose I want to look at the relationship between smoking and lung cancer, and want to use propensity score matching to select a similar group of people to study. Knowing that age, and gender are ...
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1answer
127 views

Why do epidemiologists fit the number of transmission cases with negative binomial distribution?

In the recent paper on coronavirus spread in Hong Kong, the number of individuals infected by one person (relative to all transmission cases) is fit by a negative binomial distribution. Why is that? ...
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Can I use indirect standardization with the WHO Standard World Population?

I have to compare mortality rates among countries for a variable where the age-specific mortality rate is not available, but the overall rate is. I want to use indirect standardization with the WHO ...
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2answers
121 views

Significance of epidemiological confounders in a generalized linear model

I am identifying risk factors for children snoring among several predictors with generalized linear model. With backward selection, age and sex do not appear to be significant so I removed them from ...
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Population Attributable Fraction adjusted for a variable

I am working in R tryign to estimate the population attributable fraction (PAF) for a binary outcome and 2 exposure variables that I had to coerce to become binary. I have used the "epi.2by2"...
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1answer
52 views

Stratum specific estimates in a model with an interaction term

Lets say I have a logistic regression model predicting the log odds of mild cognitive impairment (MCI) and my exposures of interest are age, education and carbohydrate intake. I expect that the ...
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2answers
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question concerning Covid infection data reported by the media

I tried searching stackexchange for existing posts about this, but I could not find them. Please redirect me if appropriate. My question is very simple, and perhaps partly related to the observations ...
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Computing statistical significance from experimental data

As described in my previous question, I am currently conducting an epidemiological study in a health institution where we investigate the prevalence of Corona virus infections by measuring the ...

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