Number of observations PreviousNext
Mplus Discussion > Growth Modeling of Longitudinal Data >
Message/Author
 Gaurav Sabnis posted on Sunday, May 27, 2007 - 8:37 am
I am doing an LGC analysis in which I have 18 respondents. I have taken their responses to the same questionnaire (with 10 questions, 5 loading on one factor, 5 loading on another) over 9 weeks. Thus I have 90 columns and just 18 rows in my data file. When i try to run the model to see how the two underlying factors vary over time, it gives me the fatal error of "number of observations not greater than the number of variables". Is the number of respondents (18) an unsolvable problem? Or is there some way in which I can make this work?

I need to know because I cant go and get more responses that easily.
 Linda K. Muthen posted on Monday, June 04, 2007 - 11:14 am
The only thing I can think of is changing your data from a wide to a long format which is shown in Example 9.16 for a growth model. There are limitations to this approach for a CFA model in that all residual variances are assumed to be the same and also factor loadings. You probably need more observations or a simpler model.
 HeSook Kim posted on Monday, April 11, 2011 - 9:08 pm
My raw data's cases are 2844. But i don't know why the following result told me that the number of observations are 1422.

INPUT INSTRUCTIONS
title: growth model
data: file is C:\Users\Public\Documents/stress study.dat;
variable: names are stsum1 stsum2 stsum3 stsum4 ax_d4 stpar1 stgr2 stper3 stape4 stmat5 strpa2 strgr2 strper2 strape2 strmt2 strpa3 strgr3 strper3 strape3 strmt3 strpa4 strgr4 strper4 strape4 strmt4 axde1 axde2 axd3 sexw1;
usevariables are stpar1 strpa2 strpa3 strpa4 sexw1;
missing are all(-999);
model:
i s | stpar1@0 strpa2@1 strpa3@2 strpa4@3;

i on sexw1;
s on sexw1;
I S ;
[I S ];
I with S;

OUTPUT:
SAMP;
STAND;
MOD(5);

INPUT READING TERMINATED NORMALLY
growth model

SUMMARY OF ANALYSIS
Number of groups 1
Number of observations 1422
Number of dependent variables 4
Number of independent variables 1
Number of continuous latent variables 2
Observed dependent variables
Continuous
STPAR1 STRPA2 STRPA3 STRPA4
Observed independent variables
SEXW1
Continuous latent variables
I S
 Linda K. Muthen posted on Tuesday, April 12, 2011 - 6:40 am
It seems that you may have more variables in the NAMES list than you have columns in your data set causing two records to be read for each observation. If you can't resolve this, please send the input, data, and your license number to support@statmodel.com.
 Abas Mirzaei posted on Saturday, February 04, 2012 - 6:16 pm
I am about to run an Autoregressive Latent Trajectory model.
since my unit of analysis is Brand, that's not easy to get too many observations.
I was wondering what is the minimum sample size or the number of observations to run the model?
 Linda K. Muthen posted on Sunday, February 05, 2012 - 10:40 am
I would say between 30-50 as a minimum. A Monte Carlo study could be used to investigate this further.
Back to top
Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action: