The phrase "as a secondary variable" is correct and usable in written English.
It can be used in contexts such as research, statistics, or data analysis to refer to a variable that is not the primary focus but is still relevant to the study.
Example: "In our analysis, we considered age as a secondary variable to understand its impact on the main outcomes."
Alternatives: "as a supplementary variable" or "as a minor variable".
Some trials involving PAH patients, when evaluating the response to different therapies, used HRQL questionnaires as secondary endpoints but reached variable results.
They also used Ferm's D-test as a secondary variable to determine efficacy and found that the treated patients needed less time for nursing care due to improved functionality.
Hence, when one assesses the efficacy of an intervention in this specific group, it seems reasonable to analyse, in additional studies, other important variables, e.g. HRQoL, as the primary outcome variable and depressive symptoms as a secondary variable among others.
Pooled analyses of lacosamide phase IIb/III clinical trials included a priori defined primary variables for change in seizure frequency per 28 days and the proportion of patients experiencing a ≥50% reduction in seizure frequency (50% responder rate); 75% responder rate was included as an a priori defined secondary variable.
Structural relations between the CAT factors as the primary independent variables, psychometric g as a secondary independent variable, and scholastic performance as the dependent variables were estimated, and the R2 change indicating the higher-order shared variability between g and scholastic performance was evaluated.
To corroborate self-reported risk behavior, we independently evaluated incident STIs as a secondary outcome variable.
This measure will be used as a secondary outcome variable.
A VAS (visual analog score) assessment of pain was included as a secondary efficacy variable.
In many studies the psoriasis area and severity index (PASI) score was used as a secondary efficacy variable.
The protocol also listed the relapse rate in the continuation phase for responders as a secondary outcome variable.
KAM angular impulse (the positive area under the KAM-time curve) will be calculated as a secondary outcome variable.
