Fixed reference points metric

Fixed reference points are verbal labels used in a scale to prevent variations in the response functions (Saris 1988; Saris and Gallhofer 2014).

• The reference points should add no doubt of its position on the subjective scale of the respondents (Saris and De Rooij 1988).*
• The reference points are necessary to assure that respondents are using the same underlying scale (Saris and Gallhofer 2014).*

• The use of two fixed reference points increases slightly measurement quality [True-score MTMM reliability and validity] (Revilla and Ochoa 2015) → YES*
• Differences are due to the freedom respondents have when no fixed reference points are stablished [Response bias through distribution comparison] (Saris and De Rooij 1988) → YES*
• Fixed reference points have a positive and significant effect on reliability and validity [True-score MTMM reliability and validity] (Saris and Gallhofer 2007) → YES*

References
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Revilla, M., Ochoa, C. (2015). Quality of different scales in an online survey in Mexico and Colombia. J. Polit. Lat. Am. 7, 157–177.

Saris, W.E., De Rooij, K. (1988). What kind of terms should be used for reference points. In: Saris, W.E. (ed.) Variations in Response Functions: A Source of Measurement Error in Attitude Research, pp. 188–219. Sociometric Research Foundation, Amsterdam.

Saris, W.E., Gallhofer, I.N. (2007). Design, Evaluation, and Analysis of Questionnaires for Survey Research. Wiley, Hoboken.

Saris, W.E., Gallhofer, I.N. (2014). Design, Evaluation, and Analysis of Questionnaires for Survey Research. Wiley, Hoboken.