Child protective service (CPS) cases concern taking children into protective custody. Generally, social services investigate and present arguments for child protective custody in court. The present study investigated a new type of cognitive bias in social services CPS case argumentation. The bias was first detected in an actual CPS investigation, where a relative difference was considered an attribute. Specifically, the bias occurs when people believe that the result of a relative measure can be used as a standard for other comparisons. The present study investigated the external validity of the bias. Participants (N = 133) completed an online within-subjects experiment where they rated the plausibility of two illogical arguments (Simple vs. Complex), and six distractor items. The simple argument was as follows: "A is taller than B, hence C is taller than B". The complex argument was an abbreviated version of the actual CPS case where the parents appeared to provide inadequate attachment with the child. Broken down, the complex argument had the same isomorphic structure as the simple argument. The results showed that complex argument was considered implausible by 53%, and the simple 79%. The same pattern was found among participants with relevant academic training (N = 42); social worker, lawyer, psychologist, and students of said topics), 52% and 83% respectively. The results are discussed in terms of a new cognitive bias, and cognitive overload.