Questions tagged [epidemiology]
Epidemiology is the study of the distribution and spread of disease or illness at the population level.
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Strange interaction term estimate in a logistic regression with a large class imbalance between exposure groups. How to interpret?
EDIT 2
In reply to one of the commenters, here is the 2x2x2 table. Y = 1 : Y = 0.
X = 1
X = 0
M = 1
9 : 73
3 : 29
M = 0
34 : 245
1,214 : 21,204
EDIT 1
In my attempts to make things simpler when ...
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Survival analysis vs Cumulative incidence vc Incidence rate for cohort with varying baseline dates
Research question:
I am interested in analyzing in R whether people with a specific level (out of four levels) of a blood parameter BP have a higher risk for developing a specific disease D.
A ...
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How to calculate Table1 for weighted data? [duplicate]
In many scientific papers, covariate balance is presented in Table 1 before and after weighting (e.g. IPTW, Overlap weights, etc), stratified by treatment group.
Continuous variables, for example, are ...
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How do you convert hazard ratios to differences in life expectancy?
How do epidemiologists convert hazard ratios to difference in life expectancy?
For example, let's say I find that the hazard ratio of all-cause mortality in City A is 1.25 compared to City B. I want ...
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Do I need to care if an adjustment variable violates the proportional hazards assumption?
I'm assessing the effect of an exposure variable on cancer risk. I am not necessarily trying to build the model that best predicts cancer risk, I am instead trying to best isolate the effect on cancer ...
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1
answer
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Calculate incidence density/ rate after weighting
How to calculate an incidence density/ rate for weighted data, e.g. using weighting methods such as matching weights, IPW, ...?
-- UPDATE 06.11.2023:
Regard the following paper as an example of ...
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How can I apply McNemar’s test in matched case control study on SPSS?
When conducting a case-control study with 120 cases 1:1 to 120 controls and examining whether they had a binary exposure prior to developing the disease. I am using conditional logistic regression for ...
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After obtaining a minimally sufficient set from a DAG, which variables should I include in the logistic regression model?
I have created a DAG using daggity, and from this DAG, two variables need to be controlled to evaluate the unbiased total effect of the exposure on the outcome. However, I'm confused about whether I ...
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Causal mediation analysis for time to event endpoints in randomized controlled trial data analysiscausal inference survival-analysis
I am struggling with a situation.
I have an RCT where there is an intermediate variable and an ultimate endpoint of survival (a time to event endpoint).
I want to establish that the intermediate ...
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1
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0
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Adjustment for confounders
I have some epidemiological data, relating to the prevalence of obesity at UK local authority level. For the purpose of exploration I want to derive the median obesity prevalence. However, I need to ...
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Converting incidence of new diagnoses to DALYs, or vice-versa
A recent Nature Medicine study looked at new diagnoses of a wide range conditions from electronic health records, for both a group with a particular exposure (here, Covid infection) and an unexposed ...
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What type of bias is this?
I have a longitudinal cohort study, with individuals that diagnosed with Disease A at "start", and they all developed Complication B at "end" in my study period (my study period ...
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0
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Why marginal odds in frequency matched case-control?
Let $D$ denote sampling with $D=1$ indicating subject being sampled and $D=0$ otherwise. $W$ denotes intrinsic variable of subjects, $X$ denotes exposure of interest and $Y$ denotes the binary outcome....
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Different results with splitting data vs. adjusting
I have a question regarding the results that I have achieved from my analysis. I'm new to statistics and the understanding of epidemiology. Please, help me interpret this better. I know what a ...
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Difference between query and distribution in causal inference
Reading the causality literature, we see the concepts of "interventional" and "counterfactual" query as well as "interventional" and "counterfactual" ...
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Is it valid to predict excess deaths on data used to fit a Poisson regression model?
I skimmed through a study: Excess Death Rates for Republican and Democratic Registered Voters in Florida and Ohio During the COVID-19 Pandemic that estimates excess death rates of Democrats and ...
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How to deal with participants recruited twice in a RDS (repondent-driven sampling) study?
I have RDS data and identified participants recruited twice during the study. How should I handle these duplicates? If I delete the second recruitment, it will disrupt the network. Can I consider the ...
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1
answer
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What is "cohort likelihood" and where is it from?
this is my very first post and I would consider myself a beginner in statistics, but I couldn't find anything about this in other asks.
I am learning about the Self-controlled case series (SCCS) model ...
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How to design study to predict development of a condition B given a condition A
Overall aim:
I have patients with a very common condition and I want to see if it is significantly associated with a reduction in a certain type of cancer between 6 months to 5 years later when ...
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Time-to-event prediction in the group with pre- and post-diagnosis records and the group without event occurrence as control
I study the triggering of the difficult form (ineffective two treatments) in patients with joint disease. In this retrospective study, we have collected the dataset of ~150 patients diagnosed with ...
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Discrepancy outputs from epi.2by2 and online calc for Odds Ratio, How to Interpret?
I'm trying to calculate an odds ratio for a table with very few cases. I've tried epitools oddsratio which I see won't work as the uniroot function error occurs due to dividing by 0.
The table is as ...
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1
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I am getting different results odds ratio packages R and I don't know which one is correct
I am having an issue with calculating the odds ratio for my variables, when I used epitab from epitools I get a different result than using oddsratio()
I have tried changing the level of reference. ...
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0
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Incidence risk vs -recalculated incidence risk from incidence rates
I am learning epidemiology and am puzzled with the following issue.
Assume we have a prospective cohort study with the following results:
1000 participants alive at baseline (N)
12 years of follow-up
...
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Fitting a model with only aggregate data for people without outcome
I am working with surveillance data - I have information on all the people who had outcome Y in a given geographical area in a given time period.
id
outcome_y
age
sex
...
01
yes
27
f
...
02
yes
84
...
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123
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Survival sample size calculation
I want to calculate the sample size for a survival study of patients with acute myeloid leukemia, with two cohorts, one receiving chemotherapy and the other not. I want an event-free survival (EFS) at ...
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0
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14
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Compute Odds ratio per standard deviation [duplicate]
I have odds ratio per unit change in variable. I want to convert it into odds ratio per unit standard deviation change in variable.
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24
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Calculating prevalence and incidence based on a given rate
I apologize for the poorly worded title, but I have a Prevalence/incidence question that got me confused
Hello all, I just came out of my epidemiology exam, and there’s this question that’s bothering ...
User1001024
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0
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Calculating mediation from total effect, mediation from interaction, and pure indirect effect?
I am conducting a mediation analysis using a 4-way decomposition method (med4way command in STATA). According to (https://pubmed.ncbi.nlm.nih.gov/30452641/), after getting the results of the 4-way ...
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0
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Confounding factor?
A simple question here,
How would you call a factor not associated with the exposition but with the outcome in a historical cohort ?
For example, I'm currently studying this article (https://pubmed....
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0
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Age Adjusted Prevalence at region level with only country-level population distribution
I'm trying to calculate age-adjusted prevalence for a bunch of different chronic diseases from hospital data in a specific area and I'm having some difficulty. I have total country level population, ...
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1
vote
0
answers
58
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Calculate standard error from confidence interval obtained for standardised incidence ratio
I would like to do a meta-analysis and pool data for standardised incidence ratio (SIR). I have the estimates for SIR and the corresponding 95% confidence interval (CI) for all studies. The CI are ...
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2
votes
2
answers
101
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Epitools oddsratio error in chisq.test
I am trying to calculate the odds ratio using the epitools package. The counts in 2 cells of my 2x2 table are $< 10$ so I keep receiving the following error "Error in chisq.test(xx, correct = ...
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votes
1
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Simpson's paradox detected via multivariable logistic regression?
This is not homework.
This is simple self-learning from real data.
I am fitting a logistic regression model as follows:
$$\text{logit}(p_i) = \beta_0 + \beta_1 race_{i} + \beta_2 x_{2i} + \beta_3 x_{...
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1
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Comparing a multi-dose drug to no drug exposure in a cohort study: Censoring events between doses
I am interested in assessing the association between the two doses of a dietary supplement on an event of interest.
The primary exposure is 'two doses of the supplement', and the comparator is 'no ...
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Which of the variables appear to be effect modifiers. When stratifying by each variable, which seem to indicate the presence of interaction?
The following graph displays five pairs of stratified odds ratios (not from the same study) with 95% confidence intervals. For this plot, assume the confidence intervals indicate whether the stratum-...
0
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0
answers
45
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Antimalarials as confounding variables in a prevalence study
I am performing a multi-level logistic regression analysis of cross-sectional survey data, and I am curious as to whether "taking antimalarials" is a confounding variable in the following ...
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1
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33
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Incorporating denominator uncertainty into a proportion
I am calculating an incidence risk (r): number of cases of a disease in a population over one year (c) divided by the total mid-year population (N).
$$
r = \frac{c}{N}
$$
Let's assume that c is a ...
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1
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How to spot a "wave" in the graph of new Covid 19 cases
In my dataset I have the daily number of new Covid 19 cases for many countries. I want to find an algorithm which will detect and calculate the number of "waves" which exist in the graph of ...
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346
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Difference between the concept of omitted variable bias in econ and epidemiology/social sciences (Elwert and Winship)
I am currently reading the article by Elwert and Winship's Endogenous Selection Bias: The Problem of Conditioning on a
Collider Variable.
However, I am however quite perplexed by the definition of ...
3
votes
1
answer
200
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Combining multiple imputation and survey non-response adjustments (IPW)
Imagine the following scenario:
A population cohort (assume no or equal sampling weights) of say 10000 people had various demographics and health factors measured at baseline $X_{base}$(with some ...
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Probability of having a disease when an imperfect test has yielded a negative result twice
I think the answer is already given by this post, but I wanted to check a couple of aspects.
A person I know developed a 'cold' after an event with many people.
Unfortunately we still have to be wary ...
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What is the optimal technique for determining statistical thresholds?
Relevant context: epidemiologists define an outbreak according to six defined stages (investigation, recognition, initiation, acceleration, deceleration, and preparation). From a local perspective, it ...
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Is there a difference between rate ratios and hazard ratios?
In Epidemiology, an incidence rate ratio is the ratio between the incidence rate in the exposed and the incidence rate in the unexposed, where an incidence rate is the number of events divided by the ...
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is it possible for odds ratios' or risk ratios' confidence interval to contain 1 and still be statistically significant?
my understanding is that if a 95% CI for odds ratios and risk ratios contains 1 then it is not statistically significant. However I have seen in studies such as https://pubmed.ncbi.nlm.nih.gov/...
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How to use poisson to predict incidence rates per 100,000?
I am trying to make predictions with a poission model to get the predicted incidence rate per 100,000 of some event. My problem is that when I compare the predicted incidence to the incidence ...
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1
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124
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Sample size calculation for a difference between two groups with clustered data
I want to compare proportions or means in two groups in a clustered sample. Suppose the sampled clusters are schools or hospitals or Census areas, and we sample from each of these an equal number in ...
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340
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Log of a log-transformed variable
I have been suggested to use the log of a log-transformed independent variable (i.e., log(log healthcare expenditure)). I am not sure how would this make sense. Is this a standard practice (in the ...
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Interpreting the fitted model outputs from a covariate-adjusted ROC curve in the AROC package
Below I have fitted a covariate-adjusted ROC curve (AROC) using a semiparametric Bayesian normal linear regression model available in the R package “AROC”. However, I am not clear on how to interpret/...
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0
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42
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How to compute marginal hazard rate from parametric survival models?
Suppose that the conditional hazard rate for subject $i$ follows a proportional hazard model in the form of:
$h_i(t)=h_0(t) exp(\beta_1X_{i1}+\beta_2X_{i2}+\beta_3X_{i3})$
$X_i$ are subject-specific ...
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Age and sex standardised incidence rates
If I were to compute age-sex standardised incidence rates based on a simple random sample of a nationwide household survey on hearing loss. Noting that this a sample not the total population, so the ...
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