In 2017 the average total fertility rate (TFR) across the UK was 1.74 children born per woman. While a rising birth rate is contributing to population growth, it remains considerably below the baby boom peak of 2.95 children per woman in 1964, or the high of 6.02 children born per woman in 1815, below the replacement rate of 2.1, but higher than the 2001 record low of 1.63. In 2011, 47.3 per cent of births in the UK were to unmarried women. The Office for National Statistics published a bulletin in 2015 showing that, out of the UK population aged 16 and over, 1.7 per cent identify as gay, lesbian, or bisexual (2.0 per cent of males and 1.5 per cent of females); 4.5 per cent of respondents responded with "other", "I don't know", or did not respond. In 2018 the median age of the UK population was 41.7 years.