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

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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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6 views

data dependent quantiles

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

Overblown Specificity

A medical test is administered with a very low threshold level with the rationale that the condition being tested carries a high mortality rate, and a timely diagnosis is critical. However acute and ...
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9 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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23 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 ...
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40 views

Estimating width of logistic prediction interval from value of fitted coefficients only

On page 1530, left column, of a study by Redline, Tishler, Schluchter, Aylor, Clark and Graham (1999) (ungated version), one reads: Because there is uncertainty regarding the optimal cutoff values ...
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24 views

Are sensitivity and specificity complement of each other?

Sensitivity : probability that a person with the condition will be classified in one's study as having the condition. ...
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14 views

Adjusting for mediating variables (everyone does it!)

I have always learned that when doing multivariable regression, one should not adjust for mediating variables between the independent and dependent variables of interest. I have seen in the academic ...
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1answer
31 views

What is the definition of “population” in Case-Control Study?

Why in case-control studies, cases and non-case are taken from "Two-different Population?" Why don't they come from a single population?
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1answer
93 views

One-sided Fisher's exact test with mid-p correction

I can't seem to find a way to achieve a test in R with all of these points: Fisher's exact One-sided (greater than, at 90% confidence level) With mid-p correction What I have found are ...
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2answers
65 views

What to call exponentiated coefficients from a Poisson/negative binomial regression of cross-sectional data

In epidemiology, exponentiated coefficients are often reported as odds ratios, relative risks/ incidence rate ratios or hazard ratios. In the analysis of cross-sectional data using Poisson/negative ...
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2answers
31 views

weighted disease prevalence in logistic GAM

I'm working on disease prevalence, something I've never done before, and I'm trying to weight a gam with population. It seems to me that the prevalence rate for China ought to count a bit more than ...
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1answer
62 views

Do I subtract end-of-year deaths from total population? (prevalence and incidence)

For calculating prevalence and incidence rates... I am not sure if I should be subtracting "deaths at end of year" from the population total/at risk? I know that incidence rate involves the the ...
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2answers
47 views

Can you compare probabilities of an epidemic by knowing R0 values?

In comparing two diseases with different basic reproduction numbers (R0), is it possible to use the R0 values to calculate the probability of an epidemic spread through a population? For example, if ...
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2answers
159 views

Comparing odds ratio of sample to odds ratio of population?

How would one compare the odds ratio of a sample to that of the odds ratio of its source population? For instance: I have child murder records/data from mortuaries for a geographical area (my ...
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36 views

Comparing Odds ratios between dependant samples?

I am in a bit of quandary with a research project: I have to compare and contrast the epidemiological picture of homicide with the media coverage of homicide in a specific geographic area and ...
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1answer
80 views

Statistical issues with aggregating annual survey data from multiple years?

I am using a national telephone survey conducted every year by the CDC called the Behavioral Risk Factor Surveillance System (BRFSS) to answer a question about breast cancer screening rate in ...
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1answer
97 views

Case-crossover method with conditional logistic regression for poisson model generated data

I would like to run a semi-symmetric bi-directional case-crossover method on some generated data using conditional logistic regression. I generated data from Poisson distribution Poiss(lambda) with ...
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1answer
44 views

Testing association between exposure and disease

In a particular example from the book Epidemiologic Research by Kleinbaum [example 15.1], I have three problems. Consider the data in table 01. These data pertain to a follow-up study concerning the ...
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48 views

How would I factor study design into relative risk?

I'm comparing various conditions versus some disease for a large stratified/clustered dataset which purports to account for the entire population after weighting -- hence the use of RR instead of OR. ...
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14 views

Estimating energy requirement

I read somewhere that a large part of BMR is explained by body weight. Using a data in hand, I used step wise regression with BMR as dependent variable and gender, age, height and weight as ...
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1answer
80 views

interpreting my own data (negative confidence interval in epidemiology)

Im trying to measure the absolute change between two means of systolic bloodpressure, and used a simple method for calculating the confidence interval between to means. My goal is to estimate the ...
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3answers
139 views

Determination of regression model

I would like to regress total energy expenditure on age, gender, height and weight.But how do I check whether this relationship is linear?
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1answer
40 views

energy adjusted nutrient intake

I have a data on 7 nutrients (intake of 150 people - 75 men and 75 women). Can i do factor analysis to derive the nutrient intake pattern? If so shouldn't each nutrient be adjusted with the total ...
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25 views

How to convert epidemiological Relative Risks (RR) to carcinogenic Inhalation Unit Risk Factor (IUR)?

Measures of effect in epidemiological studies on air pollution are normally presented as Relative Risk (RR). Classical Risk Assessment procedures (e.g. US-EPA) require instead a Inhalation Unit Risk ...
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2answers
236 views

Statistical method for modelling of disease incidence for NGO

I am trying to provide help to an NGO in the non-profit sector that is running a disease screening program: The program visits thousands of villages a year. A village has a population (on average ...
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1answer
104 views

Estimating an overall summary statistic (mean) for a value reported by ten published studies

Background I am writing a systematic review and meta-analysis of the association of exposure to X with the outcome Y. I have identified ten studies that report on this subject. This will be a ...
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1answer
114 views

Why no mention of penalized regression techniques in Applied Logistic Regression, 3rd edition, by Hosmer, Lemeshow, and Sturdivant?

Just ordered this textbook, and Wow, the complete omission of this subject from an otherwise excellent reference on logistic regression is a bit surprising. The 2nd edition was published in 2000 - ...
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How to gently introduce epidemiologists/public health coworkers to advanced predictive modeling?

Coming from a social science and epidemiology background, my coworkers were trained on least squares regression, logistic regression, and survival analysis. They like to see 95% confidence intervals ...
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32 views

Relationship between “attributable risk percentage” and “relative risk”

I refer to the text provided from http://www.healthknowledge.org.uk/public-health-textbook/research-methods/1a-epidemiology/numerators-denominators-populations below: Relative Risk "Relative ...
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15 views

Using AIC to select an upper bin for a counting variable

I have some patient data and I'm using a logistic model to explore factors that might affect a patient considered severe/not severe for a disease (the DV). Many of the variables are counts; counts ...
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17 views

Pearson r with percentages across time

Data sources: CDC National Survey of Family Growth, CDC vital stats. Population: American women aged 15-44 in 1982, 95, 2002, 2006 Sample sizes: several thousand Can I use Pearson r to show linear ...
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35 views

design and analysis of experiments

Kindly recommend some teaching material for "design and analysis of experiments" for the students of biostatistics and epidemiolody. Pls note that the students have only little knowledge on ...
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1answer
57 views

Epidemiology cohort studies question

If we are conducting a cohort study of factors associated with recurrent myocardial infarctions (MI) following the first one, should our study population at baseline include subjects who had ...
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11 views

Tests behind comparison of a sample's survival to that of the general population

In the literature there are often reports of comparisons of a sample's survival to that of the general population. Life and mortality tables are cited however the tests and statistical procedures ...
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42 views

What does “units” mean in epiR package?

From epiR manual for epi.2by2 function: units: multiplier for prevalence and incidence estimates. In examples it is set to 100, units=100. What does it mean? ...
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2answers
128 views

Prognostic factor vs. risk factor

As far i understand the difference between Risk factor and Prognostic factor is : Risk factor is the ...
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8answers
26k views

Is Facebook coming to an end?

Recently, this paper has received a lot of attention (e.g. from WSJ). Basically, the authors conclude that Facebook will lose 80% of its members by 2017. They base their claims on an extrapolation ...
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36 views

Optimal way to match cases and controls w/ multiple per strata

I need to do a matched analysis. However, I cannot find good reference for the best way of matching when each stratum may contain multiple cases and controls. As an extreme example, say we want to ...
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1answer
887 views

Making a cumulative incidence plot in R

Background I have a survival object in R called km. ...
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1answer
126 views

Purposeful selection and confounding

I conducted purposeful selection as outlined in Jewell's Statistics for Epidemiology. The log likelihood tests showed covariates, which I considered to be confounding though not significant in the ...
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1answer
123 views

penalized regression applications in epidemiology

I am seeking advice on penalized regression models for selecting covariates in epidemiological studies. A difficult tasks I face is feature selection while still attempting to account for confounding ...
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24 views

Weights for retrospective cohort data

Suppose you randomly identify individuals with a certain disease (cases) at time $T$, then you identify a sample of individuals without disease at time $T$ (but at risk for disease) in a population of ...
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1answer
54 views

Separating effects of foods and of food components in nutritional epidemiology

I have data on average long-term intake of common foods of a medium/large cohort (n=500+). It was assessed semi-quantitatively (that is, interval-censored). From these about 100 food items and their ...
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4answers
291 views

What are the case studies in public health policy research where unreliable/confounded/invalid studies or models were misused?

I am drafting a literature review on a current public health issue where data are confounded: What are common historical case-studies that are used in public health/epidemiology education where ...
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2answers
393 views

Absolute risk and prevalence?

From Wikipedia If the absolute risk in the control group is available, conversion between the two is calculated by: $$ RR \approx \frac{OR}{1 - R_C + (R_C \times OR)}$$ where: RR = ...
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2answers
378 views

What is the difference between period prevalence and incidence rate?

I am confused about the difference between period prevalence and incidence rate. Following are from Wikipedia: The incidence rate is the number of new cases per population in a given time ...
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2answers
255 views

Comparing multiple incidence rates

I asked the following question on stack overflow yesterday: Negative binomial function in R Reading comment 2, I understand that I cannot use a negative binomial modeling approach (a Poisson model ...
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3answers
231 views

Basic epidemiological models in R

To support an education project around neglected infectious diseases in Sub-Saharan Africa, I aim to estimate and report some very basic epidemiological models in R to build intuition and ...
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106 views

Is there a word for the phenomenon that the old are generally less affected by risk factors?

In epidemiology, this occurs often: Old people are less prone to the influence of risk factors. For example, the Framingham risk score, which tries to estimate cardiovascular risk, gives 8 or 9 points ...