The graph in Figure 3.40 on the next page shows data regarding the relative risk of schizophrenia among people born in different months.

a. Note that the scale of the vertical axis does not start at zero. What would be the effect of sketching the same risk curve using an axis that starts at zero?

b. Each value of the relative risk is shown with a dot at its most likely value and with an “error bar” indicating the range in which the data value probably lies. The study concludes that “the risk was also significantly associated with the season of birth.” Given the size of the error bars, does this claim appear justified? (Is it possible to draw a flat line that passes through all of the error bars?)

Figure 3.40

Transcribed Image Text:

Relative risk 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 L I L 1 T T 1 I I January February March Relative Risk of Schizophrenia April May June July August Month of birth September October November December