A comparison of two scoring procedures with the NASA task load index in a simulated flight task

Two issues which pertain to NASA task load index (TLX) application procedures and scoring techniques were investigated. One issue concerned the procedure used to combine ratings on the TLX dimensions into one overall rating. The second issue dealt with the delay of TLX workload ratings for a time period subsequent to completion of a rated flight segment. Participants flew several simulated flight missions under three difficulty levels and rated the workload either immediately following a flight segment or after 15-minute or 48-hour delays. Overall workload ratings were derived through the use of either a weighted or an unweighted combination of TLX dimensions. The results of the scaling techniques were highly correlated (r=0.94), and analyses revealed no differences between the resulting scaling procedures. It was found that the time-consuming use of weighting scales is not necessary and that delaying TLX reports up to 15 minutes does not significantly interfere with recall of workload ratings