This paper concerns the modeling of low inventory lines. Currently, most mo
dels assume that processing times are independent. We consider the differen
ces in behavior of workers in low- and high-inventory production lines. Usi
ng a laboratory experiment we show that workers speed up when they are the
cause of idle time on the line. This means that processing time distributio
ns are not independent of the size of the buffer, of the processing speed o
f co-workers, or of the amount of inventory in the system. We show that the
direction of these effects is predictable and that the magnitude is signif
icant. In particular, there is less idle time and higher output than would
be predicted using assumptions of independence. in this experiment the effe
ct completely canceled productivity loss due to blocking and starving. This
work is important in understanding both the motivation of workers in low-i
nventory systems and the implications of models of manufacturing flow lines
.