2017
DOI: 10.3126/nje.v7i2.17974
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Lexis Expansion: a prerequisite for analyzing time changing variables in a cohort study

Abstract: In a prospective analytical cohort study or a study involving a longer follow up, changing age of participants influence the relationship between exposure and outcome. Usually age at entry is incorporated in the regression model to adjust for age. However, this fails to fully explain and adjust for changing age. For this Lexis expansion, a concept by Wilhelm Lexis, allows the analyst to expand the observations as per age bands and check for confounding and interaction by changing age. Lexis expansion assumes t… Show more

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Cited by 8 publications
(7 citation statements)
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“…For the computation of LE, abridged life tables with five-year age groups were constructed, with a last open interval at age 85. The age-specific mortality rates were computed using Lexis expansion, to account for the ageing of population during follow up [38]. The DFLE and its variance were computed using Sullivan’s method [39].…”
Section: Methodsmentioning
confidence: 99%
“…For the computation of LE, abridged life tables with five-year age groups were constructed, with a last open interval at age 85. The age-specific mortality rates were computed using Lexis expansion, to account for the ageing of population during follow up [38]. The DFLE and its variance were computed using Sullivan’s method [39].…”
Section: Methodsmentioning
confidence: 99%
“…Moreover, we split each participant’s follow up time into 5-year age-at-risk bands. The effect of age during the study (age-at-risk) is more appropriate because it determines current risk rather than age recorded at the start of the study (age-at-baseline) 18 .…”
Section: Discussionmentioning
confidence: 99%
“…The associations of baseline heart rate and change of heart rate with outcomes were assessed with multivariable Cox proportional hazards models. The multivariable models were stratified for age at risk (in 5-year intervals) 18 , gender, and adjusted for established risk factors of CVD, including education, smoking status, alcohol intake status, physical activity, family history of CVD, BMI, hypertension, hyperlipidemia, diabetes. In addition, we adjusted for baseline heart rate when modeling for change of heart rate.…”
Section: Methodsmentioning
confidence: 99%
“…Time-to-event analyses were used to determine time from ART initiation to non-retention over a six-months follow-up period. Because some individuals started ART during the pre-COVID-19 period, but their follow-up crossed over into the COVID-19 period, Lexis expansion was applied and follow-up time split accordingly, either to pre-COVID-19 or COVID-19 periods [31]. Univariable and multivariable survival regression models were used to determine effect of COVID-19 period on non-retention.…”
Section: Methodsmentioning
confidence: 99%