Calculating Norm-Based T-scores From Your EORTC QLQ-C30 and FACT-G Data

Investigators and clinicians can generate subscale scores and an overall quality of life score from the EORTC QLQ-C30 and FACT-G which are sample-specific. However, the interpretation of one's results can be difficult when scores obtained in a given study are not easily referenced to a larger population.

We have developed a tool which calculates norm-based T-scores to aid in the interpretation and understanding of clinical and research data in the context of: (A) the general Australian population and (B) an Australian population with cancer.

What are norm-based T-scores?

Norm-based T-scores rescale raw scores into standardised scores with a mean of 50 and standard deviation of 10. For example, a sample with a norm-based T-score of 40 is one standard deviation below what might be expected for someone from the general population. 

Why are norm-based T-scores useful?

Norm-based T scores allows direct, meaningful comparisons of scores that are measured on different scales. In norm-based scoring, each scale is scored to have the same mean of 50 and standard deviation of 10. Without referring to actual norm values, the differences between raw scores and norm scores can be quickly and appropriately interpreted.

For example, consider a sample in cancer patients with a global quality-of-life score of 67 and a physical functioning score of 77 on the 100-point scale of the EORTC QLQ-C30. It would be incorrect to simply infer that cancer had a greater negative impact on global quality-of-life than physical functioning. From external normative data, we know that the mean global quality-of-life score is 69, while that of the physical functioning score is 89 in a general population. In relation to these norms, the negative impact of cancer would thus appear larger on the physical functioning scale (T-score of 44) compared to the global quality-of-life scale (T-score of 49).

How do I use the calculator?

Norm-based T-score Calculator for EORTC QLQ-C30 and FACT-G (XLSM, 73KB)

The calculator takes raw mean scores from the EORTC QLQ-C30 and FACT-G to provide norm-based T-scores in the context of: (A) the general Australian population and (B) an Australian population with cancer. To calculate these values,

1. Click on the appropriate worksheet (EORTC QLQ-C30 or FACT-G) at the bottom of the screen.
2. From the drop-down menus, select the sex (Females and Males; Females (only); Males (only)) and age range characteristics which match those of your sample. The mean and standard deviation (SD) of the scores obtained from the general Australian population will be updated to reflect the selected characteristics.

3. Enter your sample's raw mean scores. For the EORTC QLQ-C30, these would be the global quality of life score, functional scores, and symptom scores. For the FACT-G, these would be each of the subscales and the overall score.

4. Norm-based T-scores will be automatically calculated and graphed in relation to (A) the general Australian population and (B) an Australian population with cancer.

(Please enable macros to allow graphs to scale for ease of comparisons)

Where does the normative data come from?

EORTC QLQ-C30: The normative EORTC QLQ-C30 data for the general Australian population comes from an Australian national online survey panel, quota-sampled by age and sex to be representative of the Australian population. EORTC QLQ-C30 data was collected from 1,821 Australians between 2015 and 2016 (1). A summary of the sample characteristics can be viewed here (PDF, 42KB). As the sample was non-representative of the Australian population for socio-demographic variables and chronic conditions, the EORTC QLQ-C30 data were adjusted for characteristics including country of birth and Indigenous status.

The normative EORTC QLQ-C30 data for the Australian population with cancer comes from the Cancer 2015 study (2). This study was funded by the Victorian Cancer Agency and was conducted at Victorian hospitals in 2015. A summary of sample characteristics of the 1,719 participants can be viewed here (PDF, 14KB).

FACT-G: The normative FACT-G data for the general Australian population comes from the Queensland Cancer Risk Study (QCRS). This study was funded and conducted by the Cancer Council Queensland and collected FACT-G data from 2,727 Queenslanders in 2004 (3). A summary of the sample characteristics can be viewed here (PDF, 9KB).

266 individuals in the QCRS population (10%) had a previous diagnosis of cancer (excluding non-melanoma skin cancer), from which FACT-G data for the cancer-specific population was used.

To make these normative data more representative of the Australian general population, CQUEST hopes to supplement the current dataset with data from other states and territories. If you own FACT-G or EORTC QLQ-C30 data from the Australian general population and would like to have it contribute to the calculator, please contact us at cquest@uts.edu.au.

References

Information on the norm-based T-score calculator was adapted from the Sydney Quality of Life Office, which also reports the SPSS syntax for the calculation of FACT-G norm-based T-Scores.

1. Mercieca-Bebber R, Costa DS, Norman R, Janda M, Smith DP, Grimison P, et al. The EORTC Quality of Life Questionnaire for cancer patients (QLQ-C30): Australian general population reference values. Med J Aust. 2019;210(11):499-506.
2. Woodcock F, Doble B. Mapping the EORTC-QLQ-C30 to the EQ-5D-3L: An Assessment of Existing and Newly Developed Algorithms. Med Decis Making. 2018;38(8):954-67.
3. Janda M, DiSipio T, Hurst C, Cella D, Newman B. The Queensland Cancer Risk Study: general population norms for the Functional Assessment of Cancer Therapy-General (FACT-G). Psychooncology. 2009;18(6):606-14.