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Questions tagged [epidemiology]

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

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What is the difference between 1-year partial prevalence and annual incidence?

In cancer research, like in this article, partial prevalence is sometimes used to assess the epidemiological state of a disease in a population. The document I'm trying to understand (link, in french)...
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8 views

Prediction models with repeated testing

I have a question on which statistical models that are most appropriate for a prediction study. I have a cohort of around 100.00 persons with results from a blood test in the 1990s. Around 50% of the ...
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Question about design choice of Enbrel RWE study

Statisticians in 2015 analyzed real world data, hundreds of thousands of medical insurance claims involving people with rheumatoid arthritis and other inflammatory diseases, according to the Pfizer ...
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8 views

Estimation of outcomes when sampling coverage is limited

Set-up: Suppose I have communities $i = 1, \cdots, I$ with individuals $j = 1, \cdots, J_i$, and these $\{J_i\}$ and $I$ are known. I have individual-level covariates $X_{ij}$ and binary outcome $Y_{...
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Qualtrics and Epi Info yield different Standard Deviation values?

Uncertain if this is the correct place to post this, but I'll give it a shot. I'm a Master's Student working with a small (n=25 respondents) data set. I originally entered my surveys into Qualtrics. ...
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15 views

Epidemiological research involving age at exposure to events as a continuous predictor

I'm looking for some more sophisticated analytical methods for assessing age-at-exposure effects. The literature I'm reading typically polytomizes age into groups, which I'd like to use as a last ...
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71 views

In a survival study, is interval censoring simplifiable to midtime imputation?

In epidemiological studies, it is common that event are interval censored, since an incident case (like a new diagnosis of disease) could have happened between 2 waves of data collection. No software ...
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29 views

Comparing adjusted odds ratios in a model

I have a pretty basic question. Say I run a logistic regression model with 2 variables both dichotomous. falls= sex+stroke+depression. I get 3 different odds ratios, one for males vs females, one for ...
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12 views

Taylor Series Power Function in R

I'm trying to recreate a compartmental model from Yu et al (2017). In this model there is a expanded taylor series power function that is used that I am not understanding how to code. where W(t) = 0, ...
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44 views

Investigate whether hospital infections tend to have common etiology in the same ward/hospital

I have data from a national prevalence study on healthcare-acquired infections (HAI). I would like to know whether two patients being in the same ward (or in the same hospital) have a higher risk of ...
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1answer
43 views

Confidence interval for Population Attributable Fraction with several strata

I have used aggregated data to create a table of person-years (pys) and deaths by social class, age and sex. If we consider social class to be a modifiable factor, we can calculate the number of '...
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1answer
59 views

Calculating confidence intervals for “excess events”

I have a study that shows 100 deaths occurred in a cohort of high-risk people. Given mortality rates in the general population, you would only expect 70 deaths to occur. The standardised mortality ...
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What does the decomposition of a relative risk look like?

Say I have a relative risk of smokers that smoked 1-20 cigarettes per day. What is the mathematical identity between that RR, the RR of those that smoked 1-10 cig/day, and RR of those that smoked 11-...
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42 views

Can variable be both a moderator and partial mediator?

Is it ever possible for a variable to be a moderator and partial mediator? I have a hypothetical example, which I think shows this can be the case. But I might be making a mistake. X = Socioeconomic ...
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1answer
44 views

Odds Ratio Vs. Risk Ratio

Relative risk, odds ratio, risk ratio, risk difference - these are all measures of the direction and the strength of the association between two categorical variables. Can I use any of these four ...
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1answer
55 views

Calculate incidence rate per person or in total

For my study I am doubting about the following: First I want to present the incidence rate for patients who received an CT-scan. I thought I would just count all the CT-scans that took place and ...
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24 views

Assess sensitivity of a binary screening result across other continuous covariate(s)

I want to assess the sensitivity of a diagnostic screening test, which is a binary test (screen +ve and screen -ve). There is no continuous measure from this test - it is literally yes or no. My ...
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19 views

Estimating prevalence using correlated data from a survey

I have some survey data from a survey. One of the questions asked the survey respondent (ostensibly an adult) to list the age, height, and weight of all persons living in the household (age, height, ...
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82 views

The counterfactual model for causation

My professional training took place in the late 1990's and I don't recall hearing some of the terminology that seems nigh-universal nowadays. I believe the accepted name is "counterfactual model for ...
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149 views

How to calculate the odds ratio if one of the groups is “0” in a case-control study?

I am using R's epicalc package to calculate the odds ratio. I have these data: Real values ...
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1answer
30 views

Standard population for SMR estimation

I have deaths by counties from 1980-2010 by age and sex. I want to calculate the SMR and then map the rates. My question is what standard population should I consider. If the SMR is Yi (# deaths ...
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28 views

Age-structured SIR/SEIR binomial chain model

To make ODE models stochastic, a binomial distribution can be used to model the number of new infections, e.g. SIR/SIS [1] and SEIR [2]. The derivation of these models makes sense, as they assume ...
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2answers
136 views

Can I use rates (e.g., crude rates) as an explanatory variable (covariate) in regression?

I am working on formulating a regression problem where my dependent variable is the number of heart disease cases (count data) in a population. I am looking to do an ecological poisson-based ...
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52 views

Cohort Study Sample Size and Multiple Comparisons

I'm designing an epidemiological retrospective cohort study with a large number of exposures and outcomes, and I'm trying to figure out how many subjects I'll need in order to run all my analyses. The ...
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1answer
48 views

Logistic regression (with dummy variables)

I have some problems with question (a) and (b) of this question. For question (a), would it be correct to simply look at the p-value alone? treatment B is coded as 0, it 'disappears' in the logit ...
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30 views

Inferring incidence from prevalence

I have a data set of patients with a risk factor for disease "A", which can be of grade 1, 2 or 3. The grade is determined by a lab value, i.e. Healthy <20, <...
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Confidence intervals for Ratios of Correlated (nested) Age-Adjusted Rates

I am interested in calculating the incidence of disease in an ethnic subpopulation (denoted $X$) and comparing this with the incidence in the entire population ($\Omega$) (where $X$ is a true subset ...
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23 views

Propensity score adjustment for multilevel exposure?

I have a hospital-based cohort study (n=1,275) and want to determine the effect of receiving a particular treatment during surgery to reduce blood loss (Treatment A), and receiving a blood transfusion ...
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3answers
1k views

Why is odds ratio an estimate of relative risk?

This link says In epidemiological terms, the odds ratio is used as a point estimate of the relative risk in retrospective studies. I understand that odds ratio is calculated in case control ...
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2answers
56 views

Terminology for 'prevalence' when it's number of people and not a proportion?

'Prevalence' is usually used to describe a proportion or rate, e.g. '5% $\pm$ 2% of the population are Blue'. What do you call this when you estimate the actual number of people in a population with a ...
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1answer
44 views

Calibration of an individual-based model of an epidemic

I am currently developing an individual-based (or agent-based) mathematical model (IBM) of an epidemic. I want to calibrate the transmission parameters in my IBM to match empirical data (epidemic ...
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1answer
828 views

What's the difference between an ecological study and a cross-sectional study?

What's the difference between an ecological study and a cross-sectional study? And could you provide an example?
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1answer
41 views

A situation where to consider row totals in a $2\times 2$ contingency table fixed or not?

In a prospective study, we draw a sample of size 100 where two sttributes A and B were present. Our goal is to assess whether ...
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In epidemiology, how to perform direct standardization when demographics don't exist in some populations?

Suppose you have data on cancer incidence for different demographics in US counties. Direct standardization is a way of accounting for demographic differences between counties. If $r_i$ is the cancer ...
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28 views

Adjusting dependent variable using regression

I have seen multiple posts and studies which used fitted values from regression to get co-variate adjusted dependent variable. Here are some to name a few: 1, 2 and 3. But I don't quite understand ...
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38 views

Power of an association study / GWAS

I came across this chunk of text in this paper: The power of association studies is dependent on the variance explained by a locus; thus, for a disease that affects 1% of the population, we ...
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1answer
67 views

How to tell the likelihood of getting a false positive? [closed]

Say we have a test for a disease we are comparing with the gold standard. You are given the prevalence of the disease, which is 1%, and sensitivity, 80%, and specificity, 90% and a total population of ...
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2answers
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How much lung cancer is really caused by smoking? [closed]

On tobacco products one can often see the statistic that nine out of ten lung cancers are caused by smoking but is this number accurate? I am sceptical about this stat for two reasons. Firstly, if ...
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1answer
330 views

“Matching” with cross-sectional studies: are the samples dependent?

I am comparing the prevalence of disease in participants of two separate cross-sectional surveys. One survey is from a group of prisoners and the other is from the general population. To account for ...
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2answers
91 views

Is there a name for disingenuous correlation?

Just heard on on this segment of a Fox News show hosted by Tucker Carlson that in recent years gun ownership has gone up while gun-related violence has gone down. Just like that. Followed by the ...
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1answer
64 views

Deriving an effect size from previous literature for determining a required sample size for a clinical trial

I'm looking to do a pre-posttest RCT comparing difference of means through a t-test, however I'm completely unsure how to calculate a required sample size using power, confidence level, and ...
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1answer
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Literature on combing randomized controlled trials and retrospective studies in meta-analyses

I have read contradictory posts whether randomized controlled trials and retrospective studies can be combined in a meta-analysis. Thus, 1) I am requesting literature on this specific topic (...
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1answer
23 views

Can I use logistic (or Poisson) regression to model epidemiological data with incomplete (but generalizable) knowledge about the population?

My question has three levels of complexity, I will try to explain one by one. Please accept I am no professional in statistics and still trying to broaden my understanding. 1) I would like to ...
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1answer
77 views

Correct algorithm for detecting outbreaks in conflict data

I'm currently working on a project researching whether Google Trends can predict conflict events in intrastate conflicts. Thus I have two different datasets; the weekly Google Trends search volume ...
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7answers
788 views

Is sensitivity or specificity a function of prevalence?

Standard teaching says that sensitivity and specificity are properties of the test and are independent of prevalence. But isn't this just an assumption? Harrison's principles of internal medicine ...
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2answers
101 views

Large Cohort/Sample Size in Epidemiological Studies

Why is it important to have a large cohort or sample size in epidemiological studies?
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1answer
57 views

Return on investment for a vaccine

I have been tasked with finding the return on investment of a vaccine. The vaccine is used by farmers for their cows and the number of cows kept varies drastically between farmers (from $1$ to $1,000'...
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0answers
21 views

How would I conduct a relative risk meta-analysis, when the exposure levels in the data are presented in overlapping ranges?

For example, if I have studies observing the dose-response relationship between alcohol (g/day) and breast cancer, and the exposures are reported as heterogeneous and overlapping ranges (10-20g, 15-...
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Finding a suitable model for modelling the changes from baseline to follow-up in a cohort study

In a cohort study, a sample of children is studied at two time points ($t_1$ and $t_2$) that are several years apart. At each time point, the BMI (body mass index), blood pressure ($\mathrm{BP}$), sex,...