To view the commuting data for your region, go to Explore > Social Accounts > IxC Social Accounting Matrix. If the Employee Compensation column makes a payment to the Domestic Trade row, then there is net in-commuting into the region (more income earned by workers who work in the area and live outside the area than vice-versa). The ratio of this value divided by the Employee Compensation column total gives you an estimate of the net in-commuting rate. If the cell is empty, then the region has net out-commuting, which will show up as a payment from the Domestic Trade column to the household rows. To get a net out-commuting rate, divide the sum of these payments (across the 9 HH types) by the sum of the household column totals.
The equation below allows you to adjust IMPLAN's estimated regional commuting rate to your known regional commuting rate.
newEC = EC*[(1-userCR)/(1-samCR)]
EC = original, unmodified employee compensation
userCR = your known commuting rate
samCR = commuting rate reported in the SAM
newEC = the EC value you want to use when running the analysis
For example, if the SAM shows that the average in-commuting rate in your region is 10% but you know that for your industry it is 20%, then: new EC = $1,000,000*(0.8/0.9) = $1,000,000*(0.88888) = $888,888.
After the analysis has been run, add the difference (EC - newEC) back to your direct EC effect since by definition EC occurs at the site of employment. Since EC is a component of Value Added, you should update the calculation of Value Added to include the difference. Because payroll taxes (social insurance taxes) are paid at the site of employment, the direct effect payroll taxes in your tax results will also need to be revised to their pre-EC adjustment levels. Create a separate activity, duplicate your event but use your EC value that has not been adjusted for commuting, and perform the analysis in a new scenario. Use the resulting direct effect EC payments to social insurance as replacement values for your adjusted EC analysis and re-sum the direct effect and total effect tax impact tables. This way you correctly account for the in-commuters' direct effect, but you have also made sure that they did not generate any further local impact.