The new GMS contract came into force in April 2004, abolished the "Red Book" and led to a significant but temporary increase in some practices' income. Every practice gets a share of a total amount of money allocated towards primary care in GMS practices (the "Global Sum"). This share is determined by the practice's list size, adjusted for age and sex of the patients (children, women and the elderly have higher weights than young men because they cause a greater workload). Furthermore, the practice gets an adjustment for rurality (greater rurality causes greater expenses), for the cost of employing staff (the "Market Forces Factor"), which captures differences in pay rates between areas, (e.g., it is more expensive to hire a nurse in London than in Perth), the rate of "churn" of the patient list and for morbidity as measured by the Health Survey for England.