Questions tagged [epidemiology]
Epidemiology is the study of the distribution and spread of disease or illness at the population level.
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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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1answer
13 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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1answer
55 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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15 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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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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35 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
41 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
36 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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1answer
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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
36 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
52 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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23 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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2answers
77 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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75 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
28 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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26 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
120 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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45 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
34 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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28 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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22 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
903 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
53 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
41 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
616 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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0answers
25 views
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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24 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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34 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
61 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
273 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
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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
677 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
93 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
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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 $1,000'...
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How would I conduct a relative risk meta-analysis, when the exposure levels in the data are presented in overlapping ranges?
For example, if I have studies observing the dose-response relationship between alcohol (g/day) and breast cancer, and the exposures are reported as heterogeneous and overlapping ranges (10-20g, 15-...
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45 views
Finding a suitable model for modelling the changes from baseline to follow-up in a cohort study
In a cohort study, a sample of children is studied at two time points ($t_1$ and $t_2$) that are several years apart. At each time point, the BMI (body mass index), blood pressure ($\mathrm{BP}$), sex,...
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1answer
203 views
How is the prevalence of a rare disease estimated?
I am working in biostatistics and often have the following conversation with medics: we are talking about some very interesting, but also very rare, disease/disorder (or side effect of a drug) until ...
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Selecting controls from a case-cohort study when location is important
I am looking at the causes of a disease in cows, both 'environmental' (ie ground-drainage, bedding type etc) and 'biological' (previous disease, sex, weight etc). Most environmental variables are the ...
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3answers
192 views
Age-adjustment (and its realization with mgcv): add age as covariate to the regression or do an internal standardization?
This question consists of two - but possibly related - parts.
Question #1
We have data on the occurrence of a disease in several age groups over several years. We try to investigate the secular ...
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1answer
23 views
Epidemiology question, comparing exposures
So I'm taking one of those online Epi classes and I'm not sure how to solve this type of problem. I know its probably simple. Any guidance would be appreciated! I didn't include the 2x2 table because ...
