Independence of Results

Hello, I'm wondering if there would be any complications with combining the results of separate IMPLAN models. We have 5 categories that will be included in the analysis. Is summing the outputs of the models as accurate as modeling the total expenditures all at once. I tested the independence of multifamily construction and single family construction as well as oil and gas and fisheries. No non-linearity of economic impacts was shown in either test. The sums of the two separate model outputs was the same as both industries modeled at the same time. Are there any exceptions to the linearity of impact(barring an industry going below zero)? Can I freely add together the results of separate models? Thank you, Peter
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  • Hi Peter, Thank you for your forum post! You are correct, you can freely add the Output together from other Models. There will be no difference in Modeling them separate or together as you will get the same value result. There may be a difference due to rounding. Although with that said, there are a few considerations when adding Outputs from different Models. You will need to ensure that your Models were built using the same data year and thus the same sectoring scheme. Also that your Scenarios were built using the same Dollary Year for View! Another consideration when adding your Outputs together to get a total impact is how you report your results. If you are looking at a Construction and Operations impact, since Construction is a one time occurrence and Operations is year over year, you will want to state this in your report. Otherwise you will overstate your impact to your audience. If you also provide a total Employment value and looking at a Construction and Operational impact, it is important to note in your report that the jobs in Construction are supported and short term rather than Operations where it is typically created and long term. In regards to Construction Employment, you would not want to sum this across the years. You also wouldn't want to add impacts that may overlap, such as an ethanol plant's production at it's value of production and the corn Sector that supplies it with the level of corn they purchase, because that would lead to double-counting. In order for us to be sure there are no additional caveats; however, we would need to know more about the types of impacts you are summing together. Thanks!

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