ABSTRACT
Another common challenge encountered by analysts is missing information. This could be due to above-mentioned privacy regulations, due to missing records, or simply because they are not recorded with smart card data. In particular for pre-paid smart cards there are usually few or no socio-demographic information recorded. Chapters 3 and 5 in this book will discuss some probabilistic approaches to overcome such challenges. Further important information may not be recorded due to the fare system. For example, bus companies that adopt flat fare systems only record either the boarding or alighting bus stop since there is no need for passengers to tap in and out. Also, in subways where ticketing gates at stations are common among lines, information on the routes taken by travellers may not be recorded as will be discussed more in Chapter 4. In summary, though some of these missing information constraints can be overcome, in many cases more analysis processes are often required before the data deliver some useful information.
