Questions tagged [change-scores]

A single variable calculated from a variable measured at two different times (post - pre). Also called "gain-" or "difference-scores". Can also be used for other analysis of pre- and post- data.

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54
votes
5answers
58k views

Best practice when analysing pre-post treatment-control designs

Imagine the following common design: 100 participants are randomly allocated to either a treatment or a control group the dependent variable is numeric and measured pre- and post- treatment Three ...
28
votes
6answers
8k views

t-test for partially paired and partially unpaired data

An investigator wishes to produce a combined analysis of several datasets. In some datasets there are paired observations for treatment A and B. In others there are unpaired A and/or B data. I am ...
40
votes
8answers
39k views

Is it valid to include a baseline measure as control variable when testing the effect of an independent variable on change scores?

I am attempting to run an OLS regression: DV: Change in weight over a year (initial weight - end weight) IV: Whether or not you exercise. However, it seems reasonable that heavier people will lose ...
2
votes
0answers
76 views

Variance of difference of $x_{i,t}$ and $x_{i,t+1}$

We have $n$ observations of human performance before and after a training program. We have a random sample of $n$ individuals and assume population distributions are normal. We thus have: $x_{1,t},\ ...
8
votes
3answers
5k views

Is it valid to use a difference score as an independent variable in a regression analysis

I would like to see if the difference in the number of BPD symptoms from baseline to follow-up two years later can predict psychosocial functioning at the 2 year follow-up. So I wanted to do a linear ...
10
votes
1answer
23k views

Is there a quick way to convert z-scores into percentile scores?

Does anyone know of a function or R package that can help me turn z scores into percentile scores? The final goal is to classify or rank a group of respondents into four categories based on the ...
1
vote
2answers
715 views

Help with change scores and/or ANCOVA design

I am carrying out an evaluation for an intervention using secondary data. Unfortunately the design of the study is weak as participants cannot be randomised. I am looking to see whether the ...
7
votes
1answer
3k views

Effect of baseline on change over time in mixed models?

I was wondering whether and how it is possible to model, within some sample, change of outcome over time which is dependent on the baseline value of this outcome, using a mixed model? Imagine, for ...
3
votes
2answers
415 views

Paired t test-like solution in a two-group pretest/posttest design

I am analyzing a dataset where pre/post measurements are made (before/after a surgery) on patients who can belong to two groups, and we are interested in how group membership - let's call it G - ...
1
vote
1answer
477 views

paired t-test as a simple latent change score model

UPDATE: This problem was (embarrassingly) solved by specifying the intercept in the regression equation as shown below: ...