For fact sheets in the WSU Extension publication series on Trends in Washington Organic Crop Production, three general types of data were calculated: Aggregate (Ag), Market Average (MA), and Grower Average (GA) values.
For all calculations, N equals the number of observations from all farms reporting for the given parameter(s). Note, N is not the same for all parameters due to incomplete or outlier data. The N for Market Average and Grower Average was generally lower than for Aggregate, because only farms that reported both parameters needed for the calculations (for example, production and acres) were included.
The calculations below use “lb,” or pounds, as the unit of production. This unit will vary with the crop under consideration. Substitute the appropriate unit in total production Q (units), average yield (units/acre), and average price ($/unit). Other units include, for example, tons, hundred-weight, bushels, cartons, cases, and flats. Standard units and conversions can be found in the USDA Fruit and Vegetable Market News Users Guide: http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5048679.
1) Aggregate (Ag) by crop by year, where “aggregate” refers to summing a variable across all growers for a given year.
*or the appropriate unit for each crop. (See explanation above.)
2) Market Average (MA) values for yield (Y, lb/ac), price (P, $/lb), and gross revenue per acre (R, $/ac) were calculated as the aggregate value of one parameter divided by the aggregate value of another parameter. N equals the number of farms where both parameters (for example, production and acreage) were reported. Aggregate values used in the Market Average calculation were based on a smaller N; thus the numeric value of AgA, for example (calculated above), may have differed from that used in the formulas for Market Average.
3) Grower Average (GA) values for yield (Y, lb/ac), price (P, $/lb) and gross revenue per acre (GAR, $/ac). Here, N equals the number of farms where both parameters (for example, production and acreage) were reported.
The aggregate value represents the statewide total for a given data series in a given year; for example, the total farmgate sales value of raspberries in 2010. The market average and the grower average differ in use and interpretation. The market average captures the typical price for a unit of raspberries sold in a given year, which is done by weighting the price that a grower received by the amount they sold. This value is likely to be more relevant for larger farms as well as for processors and retailers.
The grower average first calculates the average value for each grower in a given year, and then takes the average of all the grower values. This means that it does not weight each grower by their volume. It is likely to be more useful for prospective growers who do not know how they will do relative to other growers, but want to see what yields, prices, and gross revenues per acre have been like in recent years.
The numerical difference between market average and grower average is accentuated when a small number of growers account for a large portion of total production and they tend to receive a price different from what other growers receive. Also, variability across growers by year can be calculated using the grower average data, which is not possible with the market average data. The grower average four-year mean, median, and standard deviation (SD) were calculated for yield, price, and gross revenue per acre. The n reported for these summary statistics (in the Grower Average tables) is the number of observations by crop combined for all years, and varies by the parameter being analyzed.
For more information and statistics about organic production in Washington State, please visit http://csanr.wsu.edu/trends-in-washington-agriculture/organic-statistics/.