Questions tagged [clinical-trials]
Clinical trials are studies designed to test the safety and efficacy of new clinical interventions such as drugs or medical devices.
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Calculate odds ratios and P-value for interaction across multiple separate subgroups
I'm trying to understand/replicate an adjusted logistic regression analysis where a treatment effect is estimated separately in a number (>2) of subgroups and estimating an overall P-value for ...
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25 views
How do I divide a density/frequency plot?
I have a frequency plot, which is essentially a smooth histogram. There are three very clear features (divided with a line by eye). Please note, there are two groups, male and female. The data used to ...
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A multi-armed bandit problem in clinical trial
Suppose that we have two drugs A and B with levels $i=1,\ldots,I$ and $j = 1, \ldots, J$, respectively. These two different drugs are given to patients in a clinical trial. $p_{ij}$ is the prior dose ...
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2answers
105 views
Cox proportional hazard analysis with non-uniform samples; power analysis
We have a study involving 10,000 patients, 5,000 of them treated with drug A and 5,000 with drug B. We want to know if drug A is more effective than B. The median time to event (death) after treatment ...
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1answer
20 views
sample size calculation in 3-arm survival analysis
In a 3-arms clinical trial, with time to event data, either A is superior to C or B is superior to C it will be considered significant. No need to compare A and B.
I know how to calculate the sample ...
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12 views
Chi Square embedded in an ANOVA model?
I have treatment->outcomes count data, which is obviously modeled by a chi squared, but there are several separate ones, let's say 3. I could run 3 separate chi squares, but I want to ask what would ...
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1answer
31 views
MCMC sampling with a probability density function that have potential negative values
My question might be quite strange, but I will expose you the complete issue in order for you to help me.
I am in the context of a parallel randomized clinical trial which aim is to compare two ...
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1answer
61 views
How to calculate treatment effect and its confidence interval for subgroups in a clinical trial using Cox regression models
Plenty of literature exists on how to interpret subgroup analyses in clinical trials. One example is in this thread. Unfortunately, I have not found any paper explaining how to perform a subgroup ...
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7 views
Medical or Intervention Study
A friend and I are trying to better understand proper design of a randomized trial, from beginning to end, with an eye to creating an informal one showing the benefits of a particular academic ...
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1answer
78 views
Warnings during propensity-score matching: 1: glm.fit: algorithm did not converge 2: glm.fit: fitted probabilities numerically 0 or 1 occurred [duplicate]
I am doing a propensity score matching(nearest neighbor matching) in R with simulated data and I keep getting the above warning messages. please I need help.
The following is my code
...
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21 views
Applying the Pocock boundary rule when p-value is not set to 0.05
I would like to set my new p-value threshold correcting for both multiple comparisons and interim analyses.
In a very easy example with two analyses (1 interim and 1 final) according to the Pocock ...
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1answer
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Does an interim sample size re-estimation increase type 1 error if based on the overall event rate?
Suppose that a sample size is to be calculated for a trial: a presumed effect size summarizes the effect of intervention (relative risk RR $\exp(\theta_1)$), and background gives the rate of events in ...
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25 views
Sample size equation based on clinical paper
Hoping this one is easy, but I've been struggling to try to find what approach is being used online.
I'm trying to replicate the powering of a clinical trial for research purposes based on the below ...
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39 views
Poisson Gamma Distribution in R - Creating Enrollment Modeling Curve
I'm trying to create an enrollment curve for a clinical trial based on the following variables: Country start up timelines (staggered), Number of sites, Number of total subjects needed, Number of ...
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1answer
12 views
Testing for the significance of treatment on intervention/target group compared to control group when group sizes are different?
So I have have been conducting an experiment of an interesting feed on livestock.
So essentially what I have done is, divided the total livestock $N$ in two different sized groups $n_1 $ and $ n_2$. I ...
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0answers
25 views
How does one perform a conditional power analysis?
Suppose a test statistic $Z$ will be compared to a standard normal distribution to evaluate whether a $p$-value achieves a statistically significant result at the $\alpha$-level. Based on an ...
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0answers
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Terminology when after inclusion to a RCT patient may undergo two different randomization procedures
I have trouble finding appropriate terminology for the following.
I want to investigate treatments A and B in disease X and treatments C and D in disease Y.
Diseases X and Y are basically two ...
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17 views
“Matching” groups in a clinical study
I have the following question regarding a clinical study in the Surgery department of an hospital:
1) I have two groups of patients: group A - comprising patients operated in 2016; group B - ...
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1answer
32 views
How can one summarize categorical variables with frequency variables in a clinical study?
Quote:
All eligible patients were analyzed. For the background of the patient population, categorical variables were summarized with the frequency and rate and continuous variables with fundamental ...
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Simulating survival meta-analysis data (with a random effect) [closed]
I would like to simulate survival meta-analysis in clinical trials on R but I'm not pretty sure of what would be the best way to do it and what would be fitting more the reality.
The data would ...
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0answers
7 views
phase 1 dose and schedule optimisation methods
Braun's 2007 Bayesian method describes simultaneously optimizing dose and schedule of a new cytotoxic agent (in a phase 1 clinical trial) https://journals.sagepub.com/doi/abs/10.1177/1740774507076934 ?...
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40 views
Calculating Sample Size for Cluster Randomized Trials with Person-level or Cluster-Level Outcomes
I have been looking for a formula to calculate the estimated sample size for a two-level cluster-randomized controlled trial with cluster-level outcome data. To my reading, several authors do not make ...
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Randomization in clinical trials
Randomization in clinical trials is a phenomena where each individual has equal chance to receive a treatment. How can you express randomization mathematically.
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1answer
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How to name a bias that is not quite the “immortality bias”
Strange question from me, but try to follow me.
I do not remember or name correctly a type of bias in cohort study which is pretty clear in my mind. I try to explain:
Let's assume that I want to test ...
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1answer
20 views
Propensity Score for observations in RCT study
In theory what would the $e_i$ (propensity scores) be, for $n_i$ observations already randomized into various treatment groups ?
I know $e_i$ (propensity scores) are calculated for $n_i$ ...
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2answers
142 views
Who is right, the statistician or the surgeon?
Consider the case described below, from Peacock (1972). This passage seems to imply the young statistician is making a smart, correct statement.
But is he?
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Exploratory Factor Analysis for Smoking cessation RCT?
So I'm planning a RCT where I'm evaluating a smoking cessation application intervention vs usual care among adolescent smokers.
For my statistical analysis I'm looking at the point prevalence of ...
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1answer
64 views
Average treatment effect using relative risk difference?
So I'm designing a RCT to evaluate the effectiveness of a smoking cessation intervention. For my analysis I've decided to look at three different things. 1) the point prevalence of smoking cessation ...
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1answer
78 views
Calculating trial size with the pwr package (R)
I'm attempting to calculate n for a trial in medical imaging comparing two different imaging modalities. I've never done this before, so I'm not sure how to approach this and interpret the result.
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0answers
9 views
Choice of model for prognostic value of asymptomatic recurrence detection
I am involved in the final step of a project that evaluates the prognostic value of asymptomatic vs. symptomatic recurrence detection; all subjects experienced recurrence.
The project proposed a ...
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2answers
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Does Intention-to-treat apply to the cases that should have been excluded but not able to do so during recruitment?
I am working on a pharmacist-supported new medicine randomised trial. One of the criteria during the recruitment was that if a patient used medicine previously, he/she should not be recruited.
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0answers
20 views
How to understand a before-after effect in a longitudinal medical dataset
I am after some suggestions on what statistical analysis I can perform to show a before-and-after effect in a longitudinal electronic healthcare record (EHR). I have N number of EHRs, of varying sizes/...
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0answers
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What role(s) does Statistical Computing / Computational Statistics play in Clinical Trials?
I am going to pursue a PhD in Statistics, and the two fields that I am really interested are Statistical Computing / Computational Statistics and Clinical Trials (mainly because I like doing ...
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1answer
48 views
Per protocol or Imputation when missing is small (<5%)
if ~2% of my data is missing on the outcome (continuous scale), out of a total of 200, two in control and three in intervention group, do I need to impute?
Or can I make a case that with such small ...
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1answer
20 views
gender specific treatment arms in clinical trial
if we were designing a clinical trial to compare an old and new treatment and there was strong a priori evidence of a treatment gender interaction (ie new treatment does better than old in men, worse ...
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2answers
84 views
Why are p-values in clinical trials often based off of LSmeans
Very often I see clinical trials quoting p-values based upon the differences in treatment effects using the LSmeans. To improve my understanding of this
I attempted to learn how to calculate LSmeans ...
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29 views
What is the minimum number of post-baseline time points for a mixed model?
I have 200 case and 200 control patients. There's a baseline time point (n=400) before the intervention began, 4 months later is the first follow=up, one year later is the 2nd follow up, for 1200 data ...
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0answers
17 views
Comparing continous data for two groups over time
I am investigating the effect of drug administration on white blood count (WBC) and neutrophil count (e.g. two continuous dependent variables). Participants are divided into 1. Responded [e.g. symptom ...
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1answer
534 views
Chi Square versus Poisson distribution
In a study which analyses the effect of Lithium on suicide rates, the results were the following:
Placebo group: 3 suicides in 83 patients
Lithium group: 0 suicides in 84 patients
My first approach ...
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0answers
16 views
Is it possible to exploit the fact that a donnor gave to multiple receivers?
I have some medical data on oocyte donors and receivers. My goal is to know what factors (donor age, bmi, ... receiver age, bmi, ...) can be used as predictors of success. With "success" being a ...
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0answers
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How does the “Carlisle method” work? (used to detect improper randomization in studies)
The NPR news article Errors Trigger Retraction Of Study On Mediterranean Diet's Heart Benefits refers to something it calls the "Carlisle method" of analyzing results of published studies to look for ...
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0answers
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The Mediterranean diet - statistics issues with the updated paper
In 2013, a group of researchers published a paper with results on a randomized trial of the Mediterranean diet, finding that it appears to have significant health benefits. Today, they retracted ...
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1answer
62 views
Systematic allocation of treatment: is there a chance of biasing a design?
When we speak of the benefits of randomization, we talk about the balance of covariates so as to mitigate the possible confounding due to selection of treatment. That is, if a design were replicated ...
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1answer
175 views
Stopping rules in group sequential designs
I have read that in group sequential designs, having a maximum of $k$ stops, for the $j$-th stop $j < k$ there are 4 bounds chosen $a_j,b_j, c_j, d_j$ such that the three decisions are considered. ...
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0answers
56 views
Power calculation in exponential survival model with varying follow-up duration
Suppose I have a clincal trial where I use an exponential survival model to compare the effects of two treatments. Patients are recruited over a time interval of two years. Ideally, I would have a ...
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0answers
24 views
How does randomisation balance known and unknown heterogeneity?
Randomised controlled trials are understood to balance known and unknown heterogeneity across groups. Beyond the a posteriori point that 'randomisation looks like it balances groups' how do we know it ...
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3answers
148 views
“Pragmatic” trials: what are they?
On twitter, a trialist Stuart Nicholls critiqued a recently published study by saying:
Further to the very interesting paper by Dal-Re they flag several examples that question usage of the term ...
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0answers
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Understanding interim analysis and alpha spending functions
I have to perform an A/B test with interim analysis and found some literature about methods designed to preserve the global Type I error rate by adjusting the $\alpha$ level for each peeking.
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Sample size re-estimation in an adaptive seamless phase II/III trial with interim analysis
I have an adaptive clinical trial that includes these elements:
Seamless phase II/III: phase III follows immediately after phase II ends. Phase II has a different endpoint than phase III's endpoints.
...
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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 ...
