RESEARCH NOTE: SOME ASPECTS OF VARIABILITY AND SEASONALITY IN FOUR FRESH PRODUCE MARKETS

This study involved an investigation into the variability and seasonality in prices and quantities of five fresh vegetables (potatoes, tomatoes, onions, cabbage and carrots) sold on the four largest national fresh produce markets (Pretoria, Johannesburg, Cape Town and Durban). A variability index based on the coefficient of variation was used throughout the study. The results were based on monthly data for the period 1980 through 1993. Prices were generally found to be more variable than quantities. The five vegetables investigated were subject to a similar degree of variation in quantity. Potatoes and tomatoes were subject to substantially less price variation than onions, carrots and cabbage. The data were seasonally adjusted by means of the Census X-11 method and the variability in seasonal adjustment factors was subsequently calculated. The prices of the five vegetables were subject to substantially more seasonal variation than the quantities. However despite significant seasonal variations in the quantity and particularly the price of fresh vegetables, "nonseasonal" (random) variation still dominates the overall variability in the data