ESTIMATION OF DEGREE-DAYS USING TEMPERATURE DATA RECORDED AT REGULAR INTERVALS

Degree-day (DD) estimates based on different numbers of daily temperat ure readings recorded at regular intervals were analyzed for precision and bias. Given a temperature threshold below the daily minimum, one median standard deviation was 0.067 + 0.103, -0.043 (95% confidence li mits) DD. Bias in the degree-day estimates was detected as a function of time of year, and the relative position of the threshold between th e minimum and maximum temperatures, however, the bias was less than 0. 030 + 0.00193 (SEM) DD per day. Hourly temperature data provided a bet ter estimate of degree-days than mathematical functions fit to minimum and maximum temperature data. Use of mathematical functions results i n function specific bias that changes with time of year. In those inst ances where the timing of phenological events has been based on a part icular function, continued use of the function is necessary for consis tent results.