Questions tagged [pre-post-comparison]

Comparisons before and after an event or experimental intervention. Includes BACI (before-after-control-impact) studies.

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which SD for Cohens D in psychotherapy pre-post study?

I'm reading a study where two groups receive two different psychotherapeutical treatments. The authors calculated Cohens D: 'In addition, we report estimates for Cohen’s d effect sizes as the adjusted ...
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Analyzing Pre- and Post-Survey Ordinal Data [duplicate]

I asked 293 participants to complete a pre and post-survey after a campaign. Two hundred ninety-three people responded to the pre-survey, and 254 responded to the post-survey. The responses are ...
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Cronbach's alpha for knowledge pretest-posttest / control and treatment groups

I am having trouble finding clear answers to these specific questions about calculating Cronbach's alpha. For my dissertation study, I conducted a teaching intervention. I administered a pretest and ...
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Is it reasonable/possible to use pre-scores as predictors of change?

In change analyses (of any variable, from pre to post) we usually controll for the pre-score, as it may affect the rate of change. However, what if I am especially interested in the effect of the pre ...
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Pre-post analysis with different number of pre and post measures at different time points [closed]

I'm trying to show the effect of an intervention. A group of about 30 individuals could hardly move their arms (because of traffic accidents). One surgery intervention was performed on each individual,...
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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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Marginal Homogeneity results zeroes on the off diagonal (in R)

I am performing an analysis and am using marginal homogeneity/stuart maxwell for the first time. It is a pre-post test and in analyzing secondary outcomes I ran into an issue. I downloaded three ...
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2 matched pairs and 1 treatment/control - which test so I do

Scenario: (really short version of study) I am testing whether vitamin d supplement helps with depression. First, I have two groups (all proper randomness applied) Random assignment has occurred: ...
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R model for proportional odds methodology for scale variable that allows for variable improvements

I'm looking to understand what would be the most appropriate R model for fitting a clinical dataset in which the dependent variable is the change in a 5-point scale and the end of treatment. The data ...
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Comparing Individual and Group Scores Before and After an Experiment: Methodological Considerations

I want to compare scores before and after an experiment. However, the samples before the experiment consist of individual scores, while the samples after the experiment are composed of groups of two ...
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Comparability of means for non-normal distribution and small sample size

I have to perform a comparability study between pre and post change of a production process. I'm using the final purity to measure comparability and wanted to compare medians between pre (n=40 runs) ...
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Statistically testing for differential attrition in R?

Context I have a randomized controlled trial with three groups and three time measurements (pre, post, follow-up). I noticed that from pre to post, and then from post to follow-up, the attrition rates ...
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Is new value coming from the distribution of the previous points?

I have a set of 30 data points, measuring percent of acknowledgement of an event that should not happen. So ideal value is 0.0 but we are getting some values greater than that, of order $10^{-5}$. It ...
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Is it correct to compare values relative to baseline with a paired Student's t Test? Is this a one sample Student's t Test?

I want to analyze data from same patients in two timepoints. The problem is the measurements have high variability between patients and it makes more sense to first adjust the observed value to the ...
WojciechF's user avatar
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Best procedure? PrePost - TreatmentControl | negative slope for low Post, positive slope for high post expected. + control variables

I'm looking for the best procedure for my case. I have a Pre and Post measurement in Treatment and control group. I have a couple of demographic variables which need to be controlled for. The catch ...
Raphael Huber's user avatar
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Compare change in biomarker in two groups at two timepoints - which test should I use?

Here is a question for which I did not find a definitive answer here. So suppose I have two non-randomised group (i.e. observational data), A and B. I have measured a biomarker (named "C") ...
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Can I do a multilevel analysis for my study?

Some details about my design can be found below: There are 2 groups: Group 1 and Group 2. There are different numbers of people in each group. A pre/post (measurement) of stress is taken several ...
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On the success or failure of an experiment

Recently I've been asked this question and I wasn't really able to give a solid answer from a statistical standpoint. I hope someone can help me :) Statement Let's say that in a given region, in a ...
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Anyway to transform data with a varying derivative into something that can give me comparative percent changes everywhere?

Sorry about the confusing title, I am so confused that I don't even know how to frame the question. I have a device that gives me two sets of output values depending on how I set the surface charge of ...
Dominik Duleba's user avatar
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3 answers
236 views

How do i deal with change scores (negative and positive differences) as dependent variable in regression?

I am comparing the assessments of cognitive domains in 2 conditions: either in a noisy environment or in a no noisy environment. The same people are in both conditions. My next step is to see if there ...
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Bayesian Modeling of Pre-Post Study with Counts Including Zeros in Baseline

I'm working with data from a pre-post study examining colony-forming unit (CFU) counts before and after the application of a disinfectant. My primary goal is to model whether there's a negative trend ...
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Is it possible to get a correlation value greater than 1?

I am conducting a meta-analysis on a series of studies without a control group, with pre-and-‎postoperative data (Mean ± SD). I have calculated the SD of the mean change using the reported p-value ‎...
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An ANCOVA pre-post framework for multilevel data?

I have a continuous outcome/dependent variable that is measured multiple times before and after an treatment/intervention per subject. The multiple measures are performed very closely together and are ...
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Calculating SD for Change in time

I'm conducting a meta-analysis on weight change (T2 - T0) between Group 1 and Group 2. The data I have typically looks like this: Weight (kg) Group 1 (n=15) | Group 2 (n=14) T0 65.31±16.49 | 59.06±...
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Analysing pre and post intervention MCQ results for significance- which statistical test to use?

I have ran a teaching course for students. I carried out pre and post session MCQ quizzes to evidence effectiveness of the course, however the marks collected were anonymised (data collected via ...
S Hussain's user avatar
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Non-parametric test for comparing means of 2 or more dependent variables in R?

I have a matched paired dataset (student survey before a topic was taught and student survey after the same topic was taught) where I compare the means of their answers (answers are given in Likert ...
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How to analyze experiment with ordinal DV measured pre-post exposure?

I have an experiment with 3 conditions. The dependent variable is ordinal (Likert style item on a 1-7 scale), and it was measured at 2 time points (before and after an event that all subjects across ...
barry892's user avatar
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What statistical test should be used for pre/post data (that violate ANCOVA assumptions)?

I want to assess the effect of a treatment (control vs. ash) on a continuous variable (e.g. calcium concentrations). I have two additional grouping variables that are also both categorical: location (...
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In a causal diagram where the change score $\Delta Y=Y_1-Y_0$, does $Y_1$ cause $\Delta Y$ or does $\Delta Y$ cause $Y_1$?

In Shahar & Shahar (2010), the authors argue that in a typical pre/post observational study on two longitudinal outcomes $Y_0$ and $Y_1$: the change score $\Delta Y=Y_1-Y_0$ causes the post-...
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Help deciding analyses - RCT

I am developing a proposal for an RCT. The IV/treatment has two levels - active control Vs experimental treatment. I plan on measuring EEG ERP baselines as predictor variables for treatment response. ...
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Estimating treatment effects, 2 Group Pre-Post Matched Analysis

I am trying to estimate the treatment effect for a pre/post w 2 groups design, subjects were measured on healthcare utilization 1yr before and after the intervention (non-random assignment). The ...
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How to determine normalcy for a one group pre-test post-test? [duplicate]

My study is a retrospective one group pre-test post-test on multiple variables. Not every patient in the study had scores for all of the variables, so as long as a patient had both a pretest and a ...
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Significance test for treatment when baseline of control and test groups are different

I have two groups of different sizes (control and test) and I want to measure the impacte of a certain treatment on the test group. Unfortunately, the control group has a different baseline compared ...
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Statistical test for categorical data dealing with behaviour pre/post

I am looking for help with what statistical test I should use to analyse my data. I want to know if there is a statistically significant difference between the animals behaviour before and after ...
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2 votes
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Wilcoxon Rank Test Pre/Post By gender

I am trying to compare the paired pre to post-responses in a student survey to see if gender plays a role. I was told to do a wilcoxon signed ranked test, and I can get the mean and p-value by each ...
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2 votes
1 answer
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Interpreting coefficient of interacting factors to compare difference in scores from two time points

I am working with a colleague's data from a research project comparing two groups of learners on a test of language ability. Data are repeated measures, between-subjects. Participants in each group (M ...
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confidence interval for the difference between 2 changes in proportions

I wonder if anyone can advise on how I can calculate a confidence interval for the difference between 2 quantities that are themselves a change in proportions. To be clearer if I have two groups (say ...
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What statistical analyses would you use to analyze the change across two time points, months apart?

I will be administering an early literacy assessment to preschoolers at 2 time points in the preschool year. I want to be able to examine the growth from point A to point B. I also wanted to ...
Kay Licea's user avatar
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Creating a standardized composite "score" made up of multiple continuous, dependent variables for analysis in SPSS

I am trying to evaluate how a surgical intervention (insertion of a spinal fusion cage), resulting in distance changes between two vertebral bodies, led to new symptoms (yes/no) in some patients but ...
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Treating multiple observed differences as a latent variable vs. difference in multiple latent variables

Suppose I want to model the change in some outcome before and after treatment. The outcome of interest is the change in a latent variable measured with error before and after treatment by 3 observed ...
socialscientist's user avatar
3 votes
1 answer
117 views

Can I still call this as a difference-in-difference analysis?

I have a regression which has treatment and control groups. I want to test how the treatment group (binary variable) reacts during crises periods compared to control group. The crisis variable is a ...
Eric's user avatar
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1 answer
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Testing for normality of difference between pre-post scores

I'm currently trying to decide what test to run on SPSS for my data. I am comparing the effects of 3 different interventions on trauma scores. I have both pre and post-scores.I have created a ...
Megan's user avatar
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2 votes
4 answers
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How to evaluate patient significant improvement?

Imagine the following study where we want to teach a group of $N$ patients to improve their capacity to hold their breath under the water. We have data for the patients before teaching them and after ...
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Measuring before and after results of a treatment with N people and K trials per person

Let's say I have a group of 10 students and I want to study the effect of a treatment on their memory. I will have them each take 20 indistinguishable memory tests. Then I will administer the ...
iYOA's user avatar
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1 answer
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Comparison of two groups without using interaction effect

David Spiegelhalter in Art of Statistics states the below analysis would be problematic. Can anyone give an example (real or simulated) of how this would be a problem? Measuring two groups at ...
luciano's user avatar
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Calculating Cohen's d

I have two groups (experimental and control) and a measure (an estimate of confidence) measured at baseline and at post-intervention. I have ran a multiple regression and found that the intervention ...
Outsider's user avatar
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2 votes
1 answer
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How control for a pre-treatment outcome $Y_0$ if is a strong confounder while avoiding regression to the mean bias for treatment effect on $Y_1$?

I'm facing a dilemma in a pre/post cohort matching analysis for a healthcare intervention: Matching on the pre-treatment outcome $Y_0$ (a continuous variable) will likely lead to regression to the ...
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1 vote
1 answer
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Valid to run post-hoc tests on matched data or running afoul of Table 2 Fallacy?

After completing a difference-in-differences matched cohort analysis to estimate the pre/post treatment effect of a home health nursing intervention compared to a control group, my employers are ...
RobertF's user avatar
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Comparing proportions in dynamic populations

I have an example of dataset like this: Members of insurance plan 01.01.2021 01.01.2022 <18 y. o 2100 3000 Total members 200000 230000 How can I compare proportions and define if proportion on ...
Vlad Fedo's user avatar
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Is difference-in-differences dead?

There have been a number of papers over the past 40 years supporting either change score or regressor analysis for longitudinal observational studies. However, recent papers (for example, Tennant et ...
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