This book is the right level for an introduction into the many problems that both professionals and the public have with innumeracy, especially regarding statistics. Most of the examples are chosen from various aspects of medicine. The typical physician is completely lost when dealing with even the simplest probability problem.

Examples analyzed include mammography screening, HIV testing, and various informed consent problems. There are other examples from other disciplines, such as the routine mis-representation of DNA evidence in criminal cases and the problems that many people have with simple conditional probability in risks and associations of violent behavior.

There are examples of different equivalent ways to present these situations. Some of these are much more effective at conveying information than others. For example, although mathematically identical, saying "three out of ten people will be affected" is much more effective than saying "there is a 30% chance of being affected". Far more people understand the former phrasing.

Similarly, there is analysis of how perhaps unconscious bias is revealed in the information provided in brochures used to obtain "informed" consent for procedures. There are many ways that choice of presentation will significantly bias the readers.

This book is not a difficult read. It requires only the ability to understand and work with simple fractions. But it is sufficiently rigorous for professional use and understanding.

Gigerenzer has written some other books that are fluffy pablum for the general public that fears difficult mathematics like fractions, and has written some much more rigorous statistical works on these subjects. I recommend this one as the introduction for professionals.