Tagged Questions

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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How to correctly calculate the type I error in a two-step clinical trial when stopping after the first step?

I just finished reading the following article by Berger & Berry (1988) in which they explain how subjectivity enters statistical analyses. One of their examples concerns a clinical trial with ...
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Should one adjust analyses if interim analysis is planned for an outcome other than the primary outcome?

It is widely accepted that analyses of clinical trials have to be adjusted if interim analyses are planned in order to decide if early termination is necessary due to evidence for superiority of one ...
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Diagnostic device hypothesis testing for superiority to a fixed value

I am designing a study to demonstrate that a diagnostic medical device is more sensitive than a fixed performance goal of 70%. Currently I am attempting to determine the appropriate sample size. My ...
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Null hypothesis for carry-over effect

I am looking to test a null hypothesis that there is no carry-over effect in cross-over trials. Where: I understand that the null hypothesis will be C/O effect A = C/O effect B = 0, however I am ...
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Ordered categorical variable descriptive statistics

I'm writing a report on a (fictional) randomised controlled trial, and I'm working on my first table, baseline characteristics. It's going to look more or less like this: (The values are approximate,...
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Is my RCT a cluster randomized trial with 'person-level outcomes' or 'cluster-level outcomes'?

I am going to conduct a study in a slum area with 94 catchments (clusters). They are randomly assigned one of two treatments, and then within those catchments, 10 women are randomly chosen for ...
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Comparing two or more treatments with inverse probablity of treatment weighting

I am working on a cardiovascular observational study featuring three or more competing treatments. My preference would be to conduct the analysis first using 1:1 propensity score matching, for ...
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Statistical rationale for a 3+3 design

I am starting to learn about design of experiments for clinical trials and in particular I am interested in understanding the statistical rationale for the 3+3 design used for dose escalation in Phase ...
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Type of study without groups

In a randomised control trial, true randomisation is applied to decide which subjects receive treatment. In quasi experimental trial, the randomisation is only approximate. What is the name given to ...
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3-arm RCT with black vs white comparisons

I am trying to design a 3-arm randomized controlled trial - intervention A for group 1, intervention A+ B for group 2 and control group for group 3. I would also like to look for black vs white impact ...
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Need the formula and to understand the number needed to treat

I am reading the article http://www.ncbi.nlm.nih.gov/pubmed/16214598. I am having trouble with the calculation formula (to test it / reproduce it). The relevant information is in page 1282. For those ...
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Basic & quick question about confidence interval (novice)

I'm writing a research proposal and I need to include an estimation of what kind of sample size would be adequate. I've used a calculator, and I get the result that with a 95% confidence interval and ...
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Power calculation for assessing relatively success two different predictors on a continuous outcome, Fisher r-to-z?

I'm thinking about a study where I assess the relatively predictive power of two different measures. Let's say a patient comes to a clinic on 3 different days, and 3 different measures of a noisy ...
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Difference in Group Sample Rate, not Size, based on Independent Variable

I'm working on a study that involves measuring breathing effort of an individual over short periods of time (specifically breath distention). The dependent variable is based on a new therapeutic and ...
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Sample Properties for Estimation

Newbie here. I want to estimate the nationality of a person from the nationalities of his family. I am looking for ideas/pointers for the following: How can I know if his family is a good sample ...
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How to get event hazard rates from a survfit object for sample size calculation

I want to calculate the sample size for a clinical trial (right-censored time to event data). I have data of a retrospective analysis and would like to use nSurv ...
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Why does the often quoted formula for the Flemming O'Brien alpha spending function produce 'probabilities' close to 2?

Demets and Lan, STATISTICS IN MEDICINE, VOL. 13. 1341-1352 (1994), introduce the alpha-spending approach to interim analyses of clinical trials. Concretely, they introduce the idea of choosing a ...
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why best not worst overall response is used as an endpoint in clinical trials?

Best overall response is usually defined as best timepoint response designation up to progression or subsequent therapy. I wonder why best not WORST overall response is used as an endpoint in clinical ...
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Placebo effect in randomized controlled trials (RCTs)

How does the number of intervention arms in a given RCT comparing several interventions to a placebo affect the placebo effect?
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Sample Size for Non-inferiority with interim analyses (group sequential) study

I would be grateful if you could help me with calculations of sample size if I have following data: Outcome is binary (Yes/No), main hypothesis is "non-inferiority"; There are two planned analyses (...
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Best practice when analysing repeated measures (longitudinal) pre-post treatment-control designs

[Note, I am trying to extend the advice from Best practice when analysing pre-post treatment-control designs to my own situation] I have the following common design: 100 participants are randomly ...
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Adjust for covariables even in randomized experiments?

Randomization does not guarantee balance in an experiment. Balance is the prerequisite for causality, so theres a potential for using regression adjustment in randomized experiments. This is somewhat ...
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Can I still call the study placebo controlled if I give the control treatment to the test population as well

I am studying the efficacy of a novel drug in treating a cardiovascular disease with continuous variable results being measured and statistically analyzed. Suppose the control population is getting ...
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Adjustable sample size in clinical trial

Most clinical trials I see have a fixed sample size. In some cases they have prior data that allows estimating the effect size and the variance or distribution of values, and calculate the sample ...
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Analysis of PValues Matrix

in clinical environment I'm setting up a model to identify fraudolent behaviours from specific sites, calculating for each site some aspects that could lead to a p-value (this approach is based on a ...
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Analysis of pre-post data when 2 treatments given serially to same subjects

I have following data from a cross-over trial where subjects were given 2 types of treatments separated by a washout period. For each treatment measurement was made in pre and post treatment period. I ...
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power for estimating treatment heterogeneity in RCT

Could someone point me to a good resource for estimating power for detecting treatment heterogeneity via interactions in MR? Let's assume that individuals will be randomized to two study arms. To ...
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A clinical test incorrectly identified 50/150 false positives and 23/150 false negatives.Calculate the number of true positives and true negatives

Was wondering if anybody could explain how I can calculate the answer. Would be much appreciated.
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Linear Mixed Model for Longitudinal Data: Continuous vs. Discrete Time Parameter

I would like to conduct a power analysis for a linear mixed model with fixed effects for Treatment (two levels) and Time (four ...