Author Topic: How to obtain logit based average and standard deviation values?  (Read 216 times)

Scherge

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Hi conquest community,

I'd like to obtain some statitistics for the logit distribution per item as well as for the latent distribution such as mean, average and standard deviation on the logit scale basis. Is this somehow possible to be plotted either in the wright map or as a table?
I would find this very helpful.

Thanks a lot in advance!

Scherge

dan_c

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Re: How to obtain logit based average and standard deviation values?
« Reply #1 on: May 11, 2021, 05:41:33 AM »
You can return tables of item parameters (and their standard error) as well as generate a wrightmap with the command show: https://conquestmanual.acer.org/s4-00.html#show

For example, after estimation, typing and running "show;" will generate output to the terminal. I think you are interested in the following (see the options for "table"):

2. The estimates, errors and fit statistics for each of the parameters in the item response model.
4. A map of the latent distribution and the parameter estimates for each term in the item response model.
5. A vertical map of the latent distribution and threshold estimates for each generalised item.

Is this what you are looking for?

Scherge

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Re: How to obtain logit based average and standard deviation values?
« Reply #2 on: May 12, 2021, 07:22:04 AM »
Hi dan,

thanks. To be more precise, I am looking for the attached output.

The goal is to identify the logit statistics (average, SD).




dan_c

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Re: How to obtain logit based average and standard deviation values?
« Reply #3 on: May 16, 2021, 06:20:33 AM »
This appears to be the mean and variance of the population distribution.

This information is in the show file (https://conquestmanual.acer.org/s4-00.html#show). You can output this file, after estimation, as a text file, an excel file, or directly to the screen. You are looking for table 3: "Estimates for each of the parameters in the population model and reliability estimates.".

The mean of the population is given under Regression Coefficients ("CONSTANT"), and the variance is given int he unconditional covariance/correlation matrix ("Variance"). You will need to convert the latent variance to SD and SE (note the number of cases in the model is given in table 1, see "Cases in estimation")

Note if you have a complex population model (e.g., more than an intercept-only model), then it may be easier to use the command "descriptives": https://conquestmanual.acer.org/s4-00.html#descriptives.

"Descriptives" will directly report the mean, variance, SD for you (and the error associated with each). You can also calculate other statistics, like percentiles and classification above and below benchmarks.

Screenshot is attached.



Scherge

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Re: How to obtain logit based average and standard deviation values?
« Reply #4 on: May 20, 2021, 06:41:41 AM »
You are of so much help, dan! Thanks a lot.  :)

This is what we where looking for.