der Proband
subject
A person who voluntarily takes part in a scientific study, experiment, or test; a test subject.
Für die psychologische Studie werden noch Probanden gesucht.
Subjects are still being sought for the psychological study.

subject
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subject
A person who voluntarily takes part in a scientific study, experiment, or test; a test subject.
Für die psychologische Studie werden noch Probanden gesucht.
Subjects are still being sought for the psychological study.

'Proband' comes from the Latin 'probandus' (the one to be tested). It is related to the German verb 'probieren' (to try) and the noun 'die Probe' (the sample/test). This helps you understand the meaning 'Versuchsperson' (test subject).
Die Probanden mussten verschiedene Aufgaben am Computer lösen.
The subjects had to solve various tasks on the computer.
'Proband' is a formal, technical term from science and research. In everyday language, you would more likely say 'Teilnehmer' (participant) or 'Testperson' (test person).
Die Ergebnisse der Studie werden anonymisiert und die Namen der Probanden nicht genannt.
The results of the study are anonymized, and the names of the subjects are not given.
The word is typically used in the context of scientific tests. Common combinations are 'Probanden für eine Studie suchen' (to look for subjects for a study), 'an einem Experiment teilnehmen' (to take part in an experiment), or 'eine Gruppe von Probanden testen' (to test a group of subjects).
Das Institut sucht Probanden für eine neue medizinische Untersuchung.
The institute is looking for subjects for a new medical study.
patient
'der Patient' and 'der Proband' can both be people in a medical or scientific setting. The important difference is the purpose: a patient receives help, examination, or treatment because it concerns their health. A subject takes part in a study, test, or experiment. They do not have to be ill. The words can be confused when a study takes place in a clinic. In that case, the rule is: someone being treated is a patient; someone taking part in an examination or test is a subject.

Für die neue Studie sucht das Labor noch zehn Probanden.
The lab is still looking for ten subjects for the new study.
Wegen starker Schmerzen untersucht die Ärztin den Patienten sofort.
Because of severe pain, the doctor examines the patient immediately.