

Indicators in LCA and class size 

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Hello, I would like to know if it is possible to use items and parcels as indicators in lca at the same time. I have six items which are loading on three factors (each factor has two indicators). For the third factor, the loading of the second indicator are low in comparism to the other factor loadings (.646). For the LCA I used first all items as indicators, but as the loading of the one item are low (.646), this item did not differentiate very well (e.g. in all 4 classes, for this item, persons had probabilities of more or less 55% to be in category 2). When I use for factor 3 one item and one parcel instead of the two items, the 4class solution is much better differentiated. 1) Is it ok to use an item in combination with a parcel as indicators for one factor and only items for the other factors, or does this bias the results of the classsolution? 2) Another question is, if there is any literature about the optimal size of the classes. I have one class which includes about 7.9% of the sample and I am wondering if this is too small. Thank you very much for answering. 


1) you don't want to use both an item and a parcel containing the item because then you have a direct correlation between the two variables which is not modeled in the LCA. 2) The minimum percentage of the classes is related to the sample size  a large sample allows small percentages. There is no fixed rule and only a Monte Carlo study could tell what could be well recovered. 


Thank you very much for the prompt answer. I think i was unclear, sorry. My parcel does not contain the same item as I use already in the analysis  it contains two other items, which are indicators for the same factor...(factor is measured by: item1; parcel=item2 and item3) so under that circumstances, may I use the item and the parcel as indicators? Thank you!! 


Yes. 

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