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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Predict change in dependent variable over three time points using independent variable at baseline

I want to predict the change in my dependent variable (DV) over time using an independent variable (measured only at baseline). My DV was measured at three points in time. The easiest way would be to ...
65 views

Diff-in-diff with an unbalanced panel

Say I want to study the effect of some intervention using a diff-in-diff setup. I have a panel of units observed during some period. I can identify treated/non-treated groups and pre/post periods (...
1 vote
47 views

What is the best approach to look at association between change in X and change in Y?

What is the correct approach to analyze the association between changes in two variables with two synchronous repeated measurements? I have calculated delta change scores for variables X and Y both ...
• 309
298 views

Calculating sample size for comparing pretest and post-test scores

I am trying to evaluate a new curriculum. I intend to do it by giving students a test at the beginning of the academic year (pretest) and one at the end of the year (post test). There are roughly 50,...
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Is it possible to calculate effect size from the relative pre-post change?

I am trying to conduct a meta-analysis that focuses on the pre-post change of an intervention. While most studies reported the pre and post mean and SD scores of the outcome, some only reported the ...
13 views

Effect size calculation (with CI) for proportions with a 2-arm pre-post design (i.e. experimental and control group)

I've been trying to find how to work out the effect size of an intervention that has only provided information on the proportion of participants who reported they had increased 'knowledge' after the ...
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Controlling for regression to the mean in nonparametric survey response data - pre-post design - difference between groups

I have 920 pre-post responses to 5-point Likert-scale questions evaluating the impact of an educational intervention. I wish to test whether outcomes (change = post - pre) differed across different ...
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1 vote
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Assessing bivariate change (pre- and post-intervention) when sample size is small and there is no control group?

I have data from a randomised control trial of approximately 60 people (30 people in the intervention group, 30 in the control group). I would like to assess whether change in one variable (M) is ...
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Apply Difference-in-Differences to Pre Cost Comparison

Context: There are two groups of users ('Control' and Test') that are randomly assigned at the beginning. (Let's assume they finished allocation right before week 0 and not accepting new users and ...
22 views

ANCOVA sensitivity to large variation existing in only one of the groups

I plan to run ANCOVA to test the effect of diet intervention across 3 groups. I have before and after intervention measurements and use before measurements as covariate ( ...
1 vote
27 views

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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1 vote
95 views

Difference-in-differences when treatment status is revoked

I am trying to analyze the effect of receiving "elite" status on a university's number of international first-year students. I have a perfectly balanced panel of 17 universities over an 18-...
106 views

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 ...
52 views

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 ...
1 vote
20 views

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,...
1 vote
104 views

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), ...
• 11
22 views

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 ...
13 views

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: ...
42 views

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 ...
36 views

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) ...
184 views

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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1 vote
25 views

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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631 views

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 ...
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1 vote
49 views

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 ...
35 views

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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1 vote
43 views

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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52 views

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 ...
1 vote
512 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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1 vote
82 views

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 ‎...
35 views

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±...
30 views

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 ...
1 vote
2k views

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 ...
1 vote
49 views

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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1 vote
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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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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 ...
85 views

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 ...
1 vote
39 views

Hypothesis Testing for Paired Count Data

I have the following data: For a group of patients, the number of hospital visits in a 6 month period both before and after receiving a treatment has been measured. I wish to demonstrate that the ...
145 views

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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52 views

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 ...
16 views

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 ...
160 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 ...
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433 views

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 ...
151 views

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 ...
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1 vote
162 views

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 ...
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