The present study aimed at isolating factors of potential influence on the Novel-Object Test (NOT), the Forced Human-Approach Test (FHAT), the Voluntary Human-Approach Test (VHAT) and the Human-Animal Relationship Test (HART) to draw conclusions about factors that should be considered when using these tests for the evaluation of the welfare level at different farms. Therefore, the NOT, FHAT, VHAT and HART were performed three times on ten different fattening farms. The pigs were tested at pen level, so that all pigs of one pen were examined simultaneously and scored individually during the same test. The pigs at the beginning of fattening (1) were significantly more interested in the novel object than the pigs in the middle of fattening (2) and final fattening (3) (1: 79.3 ± 0.03 % vs. 2: 66.4 ± 0.04 %, 3: 67.7 ± 0.04 % of pigs, p < 0.05), which is also reflected in the object contact latency: the animals at the beginning of fattening had a significantly lower latency than the animals in the final fattening (1: 3.5 ± 1.4 s vs. 3: 5.5 ± 1.4 s, p < 0.05). In pens in which only gilts were held, the animals showed significantly more interest in the novel object than the boars (gilts: 75.1 ± 0.05 % vs. boars: 65.0 ± 0.06 %, p < 0.05). Furthermore, the pigs at the final fattening interacted significantly less with the human than the pigs at the beginning and the middle of fattening (1: 79.7 ± 0.05 %, 2: 79.6 ± 0.05 vs. 3: 64.6 ± 0.06 % of pigs, p < 0.05) in the HART. In the VHAT, the pigs in the middle of fattening showed significantly lower latencies to come into contact with the human than the animals at the beginning of fattening (1: 11.6 ± 1.4 s vs. 2: 8.1 ± 1.4 s, p < 0.05). No significant influencing factors could be determined for the FHAT. Thus, the present results indicate that the behavioural reaction in the NOT depends on age and sex of the pigs and that different ages lead to different reactions to a human in the VHAT and HART. The reaction during the FHAT might be less vulnerable to the factors age, sex, farm size and observer.