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Response Interpolation and Scale Sensitivity: Evidence Against 5-Point Scales

Kraig Finstad

Journal of Usability Studies, Volume 5, Issue 3, May 2010, pp. 104 - 110

Article Contents


Methods

The following sections discuss the participants, materials, and procedures used in the study.

Participants

Participants consisted of 172 Intel® employees involved in the usability testing of two enterprise software applications. Eighty-four participants were surveyed in a series of tests involving a procurement application, and 88 participants were surveyed in a series of tests involving a workforce management application. Both usability tests were international in scope, with participants from the United States, England, Russia, China, the Philippines, Malaysia, Germany, the Netherlands, Ireland, and Israel.

Materials

Two versions of the SUS were used in usability testing. One was the standard SUS as described by Brooke (1996), a 5-point Likert scale. This scale was used in the testing of the workforce management application. An alternate 7-point scale version of the SUS, with 7 as Strongly Agree instead of 5 but otherwise unchanged, was used in the testing of the procurement application. This experimental 7-point version of the SUS was developed only to ensure that findings were due to the scale and not the wording in the instrument. The conditions were not alternated within software application because consistent scoring was required for the usability evaluations.

Procedure

Each participant engaged in a series of tasks involving the respective enterprise application being tested. At the conclusion of usability testing, each participant was given a verbally-administered version of the SUS, featuring either 5-point or 7-point Likert items. Participants read each survey item out loud and verbally indicated their response. The facilitator recorded their responses for later analysis exactly as voiced, i.e., regardless of interpolation. At the conclusion of the study the participants were debriefed, thanked for their participation, and released.

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