# Questions tagged [observational-study]

An observational study involves purely observing the state of the world without manipulating it.

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1 vote
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### Understanding Ignorability and Confounding Variables

I am reading Data Analysis Using Regression and Hierarchical Models and am confused by the concept of ignorability. The description in the book seems to say different things. Said another way, we ...
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### Repeated measures study design with patient drop out for blood concentrations

I am investigating the longitudinal response (course of blood concentration) to a drug in 100 patients. This is a retrospective study. For this purpose, I have blood concentrations over several ...
23 views

### Should I adjust for time for different baseline entry time in an observational study?

Suppose I have a dataset with n waves. I will select samples based on a specific criterion (e.g., wave i with event=0; wave i+1 with event=1). Therefore, each individual's entry time is different. ...
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1 vote
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### Observational pre post design and confounder adjustment

I have observational data with baseline, and two follow-up measures with a binary treatment. Dependant variable is questionnaire scale score ***. I am planning on fitting a linear mixed effects model ...
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### Can I do a meta-analysis of categorical outcomes by assigning them to ordinal values in single-arm studies?

I have a collection of case reports and single arm cohort studies (without control groups) that describe the clinical response of patients treated with a particular drug. The response is reported ...
1 vote
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### Assessing whether the probability of being assigned treatment is equal (or reasonably close) between two individuals/groups [closed]

I'm currently studying the textbook Design of Observational Studies, second edition, by Rosenbaum. Chapter 3 Two Simple Models for Observational Studies says the following: 3.1 The Population Before ...
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1 vote
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### How to use propensity scores in real examples

I am trying to understand how to use propensity score matching in a real world example (e.g. case control study). Step 1: Based on what I understand, I think a Logistic Regression is first used to ...
1 vote
48 views

### How to cope with pre-trend violations in a stacked DiD?

I want to analyze several events using a difference-in-difference approach. Since the events occurred at different times, a staggered or stacked DiD approach would be suitable. In my case, I have many ...
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### Experiments where the treatment is such that the act of applying the treatment to some people within the group and not others undermines the treatment

Let’s say we have an experiment where we want to apply some treatment to some group to test whether the treatment “works”. But the treatment is such that the act of applying the treatment to some ...
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### Should I use independent- or propensity score matching?

I work on data form an observational study (n=34) and want to compare the outcome of the individuals to an historic cohort (n=600). Subjects in the observational study received additional treatment ...
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1 vote
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### Linear mixed models with repeated gain scores in a natural experiment

Background: I‘m working on a dataset that contains observational data from questionnaires referring to a natural experiment. People were asked weekly whether they received an unexpected message (X), ...
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### How can mahalanobis and chi2-test be used to determine of an observation is acceptable?

Assume that you have a model $$\dot x = Ax + Bu$$ $$y = Cx$$ And this model is SISO. Single input and single output. You got the mission to determine of an observation is acceptable for the kalman ...
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### Bias in survival analysis: nice summary of all the different types and remedies

I am quite new to the field of survival analysis and am getting lost and confused with all the different types of bias that can occur, particularly in observational studies. For example, it appears ...
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### Best Approach to Detecting Breakpoints in Continuous Treatment-Outcome Relationship?

I am currently conducting research to understand the relationship between a continuous treatment variable and a continuous outcome variable. To mitigate confounding and selection bias, I am employing ...
248 views

### Sufficient Sample Size for Three-way Interaction from Observational Data (2x2xContinuous)

I'm wondering how one determines the sample size needed to sufficiently analyze a three-way 2x2xcontinuous (logistic) regression interaction using observational data (association study)? Any ...
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I have a dataset containing 50,000 observations of individuals undergoing drug treatment in Chile from 2015 to 2019. I aim to examine whether polydrug use (intake of more than one substance at the ...
1 vote
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### How can I control for confounding sociodemographic variables, in a correlational study with two IV's?

I want to control for the effects of confounds in an observational study (using self-report questionnaires), however, I do not want to imply a causal relationship between my two constructs. Therefore, ...
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### Confounding variables are nested with treatment, not able to be measured, how to address the influence from confounding factors?

We gathered driving data from two cohorts of drivers belonging to the same age group. The first cohort, Group A, utilized System A (treatment group), whereas Group B drove vehicles without this system ...
161 views

### How should control candidates be decided for causal inference?

I’m getting a bit confused about who to include in the control and treatment pools and would appreciate the help. I need to estimate the effect of treatment where 100% of the population was assigned a ...
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1 vote
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### How to estimate the effect of treatment duration on survival outcomes

I'm reading the paper "How to estimate the effect of treatment duration on survival outcomes using observational data"(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6889975/), and it states ...
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### Why is covariate balance fundamental for causal inference in observational data but unnecessary in experimental data?

The observational case For observational data, Hernán & Robins (2023, p. 49) state: In the absence of marginal randomization, [computing the average causal effect in the entire population] ...
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### Is this a breach of the consistency principle in causal inference?

My understanding of the consistency principle is that the observed outcome is equal to the potential outcome. i.e. let T = treatment, if T=1 then then the Observed outcome (Y) is equal to the ...
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### Comparing treatment effects across groups

I created two donation campaigns, one loss framed (N:1993) and one gained framed (N:1989) I understood donations are usually veeeery low and the sample was a lot smaller than previously expected, so ...
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### How to deal with patients falling out of the study more frequent in one treatment arm

I'm doing a retrospective comparison of two treatments (A and B) for eye disease. Both procedures have the same most common side effect (dependent variable) but their indications differ slightly ...
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### Selecting correct study design and statistical analysis for my project

I am analyzing risk factors associated with surgical site infections where we want to have a 3:1 case-control study. Other than some brief lectures in my classes, the only thing we were taught about ...
1 vote
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### Why is the fully-symmetric bidirectional case-crossover design biased and the semi-symmetric design not when there are time-trends in the exposure?

I am trying to understand why the fully-symmetric bidirectional case-crossover design is biased when there are time trends in the exposure and why the semi-symmetric design is not biased? I have tried ...
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### Observation in Quantile Regression

i have 30 observations of yearly data and i try to do quantile but results is all of my variables is not significant. im wondering if we can use quantile regression on yearly data? or is there any ...
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### Can age ever be confounded if it is the independent variable in an observational study?

This is a follow-up to my previous question: "Basic understanding of control variables in observational studies" I have understood the answer, but am still trying to figure out what I think ...
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### What does look back mean observational studies?

Consider I am doing observational study either case control or cohort in either of the following cases. Case. 1 Suppose I found enrollment/rate of population with disease is too low where disease ...
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### How to adjust retrospective-observational survival times to account for immortal time bias?

I would be very grateful for a gentle sanity check on adjusting survival times in my comparison groups. The scenario: I am using Cox regression to calculate HR risks over some covariates of interest. ...
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1 vote
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### Sample size calculation for non-inferiority prospective observational study with paired nominal data?

I'm doing a diagnostic observational study, where doctors in two different fields (emergency physicians vs radiologists) try to diagnose same patient (paired sample). The question we are trying to ...
1 vote
2k views

### MatchIt Exact Matching without replacement (1:1)

I am trying to use the MatchIt package to conduct exact matching on several categorical variables (sex, zipcode and an eligibility group code). After matching I want to have the same number of treated ...
1 vote
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I'm conducting an analysis on several hundred thousand individuals to understand if there are longitudinal differences in an outcome across clusters of the individuals. My outcome is healthcare cost (...
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### Wilcoxon signed rank for matched cohort study

I am hoping someone can help me with figuring out something I came across in this article ((https://support.sas.com/resources/papers/proceedings/proceedings/sugi29/165-29.pdf). On page 5 the authors ...
137 views

### test for difference between matched pairs in 1:1 matched study

Background: I have a retrospective study (registry) that contains data on people with kidney transplant. Among these patients, we have a very small number of people with a specific genetic disease (n=...
508 views

### The correct treatment of censorship and observation periods in survival analysis using longitudinal observational data

I have longitudinal retrospective data and want to perform Cox proportional hazards regression. Still, I would be extremely grateful if the CrossValidated community could sanity-check my understanding ...
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### Possible to have independent observations without random sampling?

Is some form of random sampling required for observations to meet the "independence" assumption of various types of regression analysis and hypothesis testing? My data (fish counts, without ...
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### Difference of baseline data between groups NOT significant on pre-matching [duplicate]

In a retrospective observational study, I'd like to compare the efficacy of drug A vs drug B, and was considering propensity score matching on age, gender, history of diabetes mellitus, and history of ...
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### Analyzing data from a non-randomized sampling design (ecological monitoring)

I have 2 questions about analyzing data that was not randomly sampled from a population. I work with "ecological monitoring" data that involves repeatedly taking measurements from the same ...
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### How to identify natural experiments?

The motivation of this question is learn what to look for in deciding whether observational data can be used for causal inference (in the sense of Pearl). Wikipedia describes a natural experiment: A ...
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1 vote
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### Does this study design lend itself to a logistic regression?

I have a cohort comprising of individuals who participate in a weight-loss program and their weight measurements are collected longitudinally for 12 months (not necessarily at the same time points). ...
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### Can I use interrupted time series analysis on irregular reported medical data?

I am interested in using interrupted timeseries analysis on real world electronic healthcare records. My understanding of interrupted timeseries analysis is that data is time-ordered and gathered at ...
• 605
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### Propensity score matching in a case-control study: can the number of matches per patient be correlated with a matching variable?

Say I am trying to investigate the association between antidepressants and achieving recovery in a depression programme. I have an observational cohort of depressed patients enrolled in the programme ...
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1 vote
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### Power calculation for observational study vs using propensity score matching estimating treatment effect

For case-control study study, one can calculate sample size to determine power of the study with respect to particular estimator of interest. Suppose I am interested in treatment effect in case ...
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### Basic understanding of control variables in observational studies

I'd like to understand the basic logic for control variables in observational studies. According to Wikipedia, one should control for confounding variables, which "in this context means other ...
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### Fixed-Effects Correlated with Another Dummy

Question regarding convention in econometrics. Suppose I am running a two-way Fixed Effect (FE) model on a District-Year panel. Year varies from 2000 to 2010. Suppose I want to examine the effect of ...
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### Comparing treatment effect using mixed effect model/gee/offset? Which one is better?

I think I have seen various posts indicating that comparison of treatment effect in observation studies should employ either longitudinal mixed effect model or GEE. Suppose each individual is given ...
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1 vote
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### Difference in Difference (DiD) estimator in cross country studies

How can we use Difference in Difference (DiD) estimator in cross country studies where we have to interpret results for each country separately? Should this be one model using country dummy and ...
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