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

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Comparing events per person years in two groups

I am trying to figure out whether occurrence of two adverse events differ or not: In one group, I have 100 adverse events in 500 subjects over 10 person-years, resulting in 0.02 events per person ...
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62 views

Sample Size and Sensitivity/Specificity [closed]

1,765 patients were given a positive/negative screening test for a disease. N = 415 patients tested positive N = 1,350 patients tested negative Due to constraints, not all 1,765 patients were given ...
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Precision adjustment in biomarker analyses

In a causal modeling framework, we are concerned with measuring an association between an exposure and an outcome. To do that, we usually fit a regression model for the outcome as the "y" on the ...
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6 views

Prevalence ratio

In epidemiology prevalence ratios is often used to show the difference between groups. Say I want to look at patients taking drug a at baseline. Some patients shift to drug b, some patients add drug c ...
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20 views

linear regression model in case-control study

if I'm conducting a case-control study and I want to use linear regression for a continuous dependent outcome. Do I have to separate cases from controls or I have to enter the full cohort to the ...
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22 views

dependent and independent risk factor

when a certain association appears only when we adjusted for certain potential confounders. In this case, can we say that this association is independent of this confounder. in my case, I'm studying ...
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1answer
55 views

Does logistic regression determine the direction of the association?

I've conducted a logistic regression in which a binary outcome was the dependent and some continuous factors were entered as independent variables. First: Can this model determine that the ...
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13 views

Minimum sample size to establish a cutoff point

I conducted a case-control study (obese and normal body weight). I want to conduct ROC curve between my variables to establish a cutoff point for vitamin depending on insulin resistance risk. Does it ...
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2answers
46 views

Odds ratio interpretation if no significant correlation between outcome and predictor

Does it make sense to conduct a logistic regression (binary outcome vitamin D deficiency and predictor CRP) if there was no significant correlation between the two variables in the first place? ...
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36 views

Study types that healthy subjects have to/can be used

What are the study types that healthy subjects have to/can be used except case-control study and bioequivalence study? Is there any other?
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16 views

reference group in logistic regression

I'm conducting a case control study. Can I use the 75th percentile of the control distribution as a reference group to compare it with the case group? and does anyone have a good reference for this?
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9 views

Conditional logistic regression interpretation and implementation

I'm conducting a case control study studying the effect of pro inflammatory biomarkers on insulin resistance among obese (cases) as compared with normal body weight (controls. cases and controls were ...
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81 views

Conditional logistic regression using SPSS

can anyone provide me with any reference that illustrates how to use conditional logistic regression using SPSS?
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46 views

logistic regression model when the correlation is insignificant

I'm new to statistics. I want to ask if i have two continuous variables with insignificant correlation between them, but when I converted one of them into binary outcome (according to its cutoff ...
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27 views

How to compute standard error of the log-hazard in the baseline arm from an n-arm study

I'm trying to use GeMTC (a package for Bayesian Network Meta Analysis) for an analysis that mixes contrast-based data (Hazard Ratio;HR) with arm-based data (event counts). The documentation specifies ...
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22 views

Adjusting confounders

I'm conducting a case-control study consisted of 32 males and 35 females matched by age and gender with controls. Do I have to control for gender when I do the statistical analysis?
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56 views

Can ANCOVA be used with a dichotomous dependent variable? If not, what have these authors done?

As stated above, if and how can ANCOVA be used with a dichotomous variable as the dependent/outcome variable? I found an article of which I wish to replicate some analyses ...
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24 views

Estimating incidence and prevalence from demographic data

I'm interested in estimating incidence and prevalence of specific diseases in the USA based on the NAMCS data set. However, the data set only records patient/prevalence visits - there is no way of ...
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43 views

Right-censored independent variable in Cox/logistic regression

I have a right-censored continuous independent variable that I want to include in a Cox regression. The variable is a physiologic test which is capped at a certain time, say 120 seconds, due to safety ...
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1answer
46 views

Why isn't it 'wrong' to use a log link instead of a logit one when doing GLM with a binomial family?

I am taking a basic biostats class for an epidemiology masters and we were recently told that log-binomial GLM is what we should be using instead of logistic regression because the coefficients are ...
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22 views

Is it possible to study the association of predicted risk of modifiable risk factor with associated outcomes

I would appreciate your help and thoughts on the following problem: I have done a study in which we made a prediction model for a disease; all analyses are performed properly and we used ...
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32 views

When do we use the term prevalence?

If I calculate at a given time, the proportion of a disease in a not representative sample of the population of study ; this proportion is called prevalence? Or just a frequency! Is there a specific ...
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73 views

confirm or validate underlining distribution association with survival analysis

The following two question outline how one can plot the results from a survival analysis using R. Q1 and Q2 But both of the examples assume, or more directly specify a weibull distribution fitted to ...
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30 views

Using person-time, instead of number of persons, for period pervalene

Let's say we want to calculate the period prevalence of Type-1 diabetes (assume treatment is always necessary) during the last year in a tourist city with highly dynamic population (a lot of in/out). ...
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173 views

Maximum Likelihood Estimate of Infection Model Parameters

I'm using the standard infection model on some data I am working with. $ dS = -\beta SI $ $ dI = \beta SI - \gamma I $ $ dR = \gamma I $ Where $S$ is the number of susceptible subjects, $I$ is the ...
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23 views

Convert categorical OR to OR per standard deviation of the exposure

I need to convert an OR for a categorical variable to an OR that represents the change per 1 SD of the exposure and I only have summary level estimates. For instance, a study reports that ...
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85 views

How do epiR's epi.2by2 functions calculate odds ratios (ORs) and CIs, and why don't they match by hand calculations?

I've seen a number of related questions using by-hand calcuations for the OR, but I'm interested in using the epi.2by2 functions in epiR. Given a 2 by 2 cross-sectional table as below (q2.m), a ...
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85 views

Should one use a censored survival model when an event is only observed at death?

A colleague of mine is trying to estimate how neutron radiation exposure changes cancer incidence rates (in mice). He has autopsy data that reports whether a cancer was observed at the time of death, ...
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42 views

Can I use the quadratic formula to calculate the cells of a 2 X 2 contingency table?

This is an extra credit problem in a biostatistics course. I am not looking for the answer, just a starting point... If you are given the following: The total sample size: (N = 200) The overall ...
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63 views

what is the biological meaning of R nought equal 1 ? endemicity?

From an epidemiological model with differential equation, we can compute the basic reproductive number R0 (the number of expected secondary case per primary case in a disease free population). ...
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49 views

Epidemiology - Pooling relative risks or hazard ratios for different outcomes from the same trial

I have one cohort trial with separate relative risks (RRs) for disease A and disease B. I would like to merge these RRs to get a single RR for diseases A+B combined. How can I do this? I have the ...
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37 views

How should I model this infection spreading problem? Is this article's solution at all reproducible?

While on the internet, I came across this quote in a Buzzfeed article, which granted, is probably not going to be the height of journalistic quality at all: This is simple math. If one person ...
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29 views

In conditional logistic regression using a mixture model, should main effects be modelled on the same subterm as interactions?

I have a question relating to modelling interactions in a conditional logistic regression model (used for matched case-control study) of the general form $$ R_i = \alpha_{s(i)} e^{\beta_1 z_{1i}} ...
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1answer
42 views

Formulating testable hypotheses

This isn't a stats question but I hope this is the most appropriate community for it. I'm writing a research proposal for an Epidemiology study. I have been told that none of my hypotheses are ...
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16 views

Power analysis for spatially structured variables in survival analysis

I am working with colleagues on an analysis of survival in a chronic neurological disease. There are several well known factors that influence survival. We have data from a good register which ...
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41 views

Censoring “Death” in Time-To-Recovery Analysis

I am performing time-to-recovery analysis comparing 2 groups. In both groups, a few subjects died from the disease under consideration (instead of recovering). Is it appropriate to consider the deaths ...
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59 views

Interpolating population data

I'm currently doing an internship where I have to calculate incidence ratios for townships for a period of 11 years. I don't have access to the population data for all years and I would like to do ...
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1answer
35 views

Separated regression analysis vs control the covariate

I am conducting a data analysis on an Epidemiology cross-sectional study. Suppose the outcome variable is an binary variable for health status (1=health, 0= unhealth). And the exposue is infection at ...
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142 views

EM algorithm to impute missing value for one variable

This is from Robert Hogg's Introduction to Mathematical Statistics 6th, exercise 6.6.5. p366, It says, Suppose $X_1$, $X_2$, $X_{n1}$, are a random sample from a $N(\theta,1)$ distribution. Suppose ...
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51 views

Repeated measurements, multiply assessed exposure with single outcome

We have data points from a prospective study in which participants were assessed 3 times during follow-up for an exposure of interest, and during a 4th follow-up they were assessed for an outcome of ...
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25 views

Non-linear population projections

First of all, I apologize if the english isn't too clear as it is not my first language. I'm an engineering student who does a lot of computer science and statistics. However what I learn in ...
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1answer
626 views

What is the difference between nominal significance and genome wide significance?

I need to determine a reasonable sample size for my Inifinium 450k methylation array case-control experiment and wondered why epigenome-wide association scan (EWAS) studies typically use a P value ...
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120 views

Comparing models using different sample sizes from the same longitudinal cohort

Epidemiological study: All of the 5 models I am comparing are derived by data from same longitudinal cohort. Each model contains the same IV, DV, and covariates. The difference between each model ...
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370 views

How to calculate the relative risk based on two independent confidence intervals

Medicine A cures 30% of patients (95% CI: 17 to 45). Medicine B cures 15% of patients (95% CI: 10 to 20). So I can divide 30% by 15% and say that medicine A is twice as likely to cure the patients ...
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53 views

Different groups, same intervention. What design is this?

I'm trying to figure out the best way to analyse the following clinical trial: Group1: Healthy individuals Group2: Diseased individuals Both groups follow the same intervention and are tested pre- ...
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89 views

compute the ratio of odds ratios and its confidence interval

How would one compute the ratio of odds ratios and its confidence interval? for example: OR1=1.07; ci=0.88-1.29 OR2=1.27; ci=0.78-1.39
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1answer
3k views

Sample size and power calculations for a randomized controlled trial

I need help with the power calculations to determine the sample size of a randomized clinical trial. This is a relatively simple trial with two arms: an intervention arm and a control arm. Patients in ...
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1answer
36 views

data dependent quantiles

Could you please explain, what does "data dependent quantiles" mean, as mentioned in the following paragraph: Quantiles appear intuitively appealing to epidemiologists as they can be thought of ...
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210 views

How to select the appropriate baseline calculation for population health studies

I'm taking over a project where I will need to create baseline measures for public health outcomes (reported annually), for example hospitalisation rates for different demographic groups. The person ...
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59 views

Is this a valid use of “positive predictive value”?

So here's your typical table for evaluating the performance of a diagnostic test: Gold standard result ...