Yield loss is the loss of a crop due to insects, bad weather and other natural factors. These are factors that apply to the entire crop, so estimating can be done by sampling and averaging. Estimating yield loss allows a farmer to estimate his actual profit at the end of the season, which will be different from the amount he could gain from all of his seeds growing perfectly. However, yield loss estimation is imperfect; the key word is "estimate."
Choose four or more spots in the field to sample from. These spots should be far apart from one another to ensure they are different.
Count all the damaged bolls in 10 feet of row.
Weigh 50-100 undamaged bolls to determine the average boll size.
Find the row width and boll size on the table (see Resources) that corresponds to your expected turnout. This number is your yield loss.