The phrase "ages were based on" is correct and usable in written English.
It can be used when discussing the foundation or criteria for determining ages in a specific context, such as historical, geological, or demographic studies.
Example: "The ages were based on the carbon dating results obtained from the archaeological site."
Alternatives: "ages were determined by" or "ages were calculated from".
Because in 1964 all gestational ages were based on the last menstruation, while in 2002 almost all gestational ages were based on first trimester ultrasound and this might influence gestational age, we controlled for birth year.
Gestational ages were based on the number of days since the mother's reported last menstrual period (LMP).
These ages were based on previous studies defining behavioural phenotypic milestones in each of the lines (Slow et al., 2003; Hickey et al., 2008).
Decisions regarding the infrastructure required for each healthy living practice for children of different ages were based on discussions with Indigenous and non-Indigenous people with wide experience of maternal and child health and housing programs in remote Indigenous communities.
This means that due to there only being 10 years of follow-up, the trajectories of the youngest cohort at the oldest ages were based on the results from the older birth cohorts who were observed at those ages during the study.
Ages are based on radiocarbon dating on 32 samples.
Absolute model ages are based on the crater production function of (Hartmann and Neukum 2001) with the crater chronology function from (Ivanov 2001).
Evolutionary theories of senescence (i.e. the increasing risk of death at older ages) are based on the fact that selection pressures on mortality diminish with age.
In brief, the assessment of the tissue AGEs is based on a technique that enlists the fluorescence properties of certain AGEs.
Estimates of gestational age were based on LMP [ 22].
Gestational age was based on last menstrual period and/or ultrasound-based estimated date of conception.
