Table 2.

Mortality in the study cohort, compared to that in the elderly population (age 65 and older) of England and Wales

Statistic*	North London Eye Study cohort	Population of England and Wales
a Death rate per 1000 PYAR	42.6
b 1 year cumulative incidence (per 1000)	41.7	56.3
c Standardised cumulative incidence	42.1
d Number of people aged 65 and older	1502	8258800
e Total PYAR	5210.1
f Observed number of deaths	222	465102
g Expected deaths if population rates applied	281.3
h Standardised mortality ratio: f/g (%)	78.9
k 95% confidence limits for SMR	67.8 to 90.1

*Calculations:

a, observed number of deaths/total person years at risk = (222/5210.1).

b, for NLES, derived from a using exp(−0.0427 × 1.0) × 10³.

For population, derived from Office for National Statistics 1996 mortality statistics.

c, calculated by direct standardisation, using the study cohort sex and age specific cumulative incidence rates, and the population sex-age structure as the standard.

f, For population, taken from Office for National Statistics 1996 mortality statistics.

g, calculated by applying the population sex and age specific death rates (Pi) to the study cohort.

k, variance of the SMR taken as 10⁴ × ΣniPiQi/(ΣniPi)² as outlined by Armitage,¹² when the purpose is to see whether the SMR differs significantly from 100% (ni is the number in sex-age group i in the study cohort, and Qi=1−Pi).