The number of school-to-work transitions may be estimated from the information in Figure 13. About 1.5 million people were in school for only part of the period. Therefore, we can infer that they may have had some activity in the labour market. These people started 2.2 million new jobs (also 1.5 jobs per individual). Some of the volatility of the labour market can be attributed to the higher-than-average propensity of young people to start new jobs. In September 1989, 52.3% of all jobs were held by people aged 16 to 34 years; two-thirds of all jobs started in the 1989-90 period were by people in that age category. Two major factors explain this phenomenon: "job shopping", whereby young workers change jobs to enhance their knowledge of the job market and look for a better fit of skills with employers' demands; and lack of seniority, which makes them more likely to be laid off. The former factor hints at a lack of knowledge about the labour market acquired while in school, as well as a lack of linkage between the education system and the world of work.