Effective Tax Rate is tax expense divided by pre-tax income (and multiplied by 100). Both tax expense and pre-tax income are for the period specified by the type input.
Formula:
TxRate% = 100 * a / b
a = IncTaxExp Income Tax Expense
b = IncBTax Income Before Taxes
This item is undefined (and will return an NA) when pre-tax income is zero or negative. Note that this item can be negative when tax expense is negative. This indicates that the company in question is enjoying tax credits or net-operating losses from prior periods. In either case, investors should expect that this is a temporary condition.