Refer to the study by Carter et al. [A-9], who investigated the effect of age at onset of bipolar disorder on the course of the illness. One of the variables studied was subjects’ family history. Table 3.4.1 shows the frequency of a family history of mood disorders in the two groups of interest: early age at onset (18 years or younger) and later age at onset (later than 18 years).

Family History of Mood Disorders Early  18ðEÞ Later > 18ðLÞ Total Negative (A) 28 35 63 Bipolar disorder (B) 19 38 57 Unipolar (C) 41 44 85 Unipolar and bipolar (D) 53 60 113 Total 141 177 318 Source: Tasha D. Carter, Emanuela Mundo, Sagar V. Parkh, and James L. Kennedy,

“Early Age at Onset as a Risk Factor for Poor Outcome of Bipolar Disorder,” Journal of Psychiatric Research, 37 (2003), 297–303.

Can we conclude on the basis of these data that subjects 18 or younger differ from subjects older than 18 with respect to family histories of mood disorders? Let a ¼ .05.