We modeled the predictors as smooth cubic spline functions given 3 degrees of freedom (df) each, with exception for the smooth function of trend that was allowed 6 df.
Absenteeism and the proportion of hours lost due to own illness or disability were modelled as a function of trend, seasonality and proxy variables for influenza activity from 1998 to 2009.
Thus, D temp =lags of monthly mean temperature D rain =lags of monthly mean rainfall D AR =lags of auto-regression (DF cases) D trend =a function of time trend (year) offset(log pop))=the DF denominator adjustment of mid-year population.
These results are primarily the function of two trends: the fall in federal tax rates and the rise of state and local taxes that are not income-based such as sales taxes.
Sensitivity to the effect estimates the flexibility of the smooth function of time trends was further tested using df of 8, 10, 15, and 20.
With the lack of progesterone in old animals, the function of Cpebs trends toward translational repression [ 55].
Time trends were estimated with natural cubic spline function, allowing a degree of freedom (df) of five per year of data using the mgcv package in R, but without penalizing the complexity of the smooth function of time trends.
LUR models explained significant variability as a function of secular trends, traffic density within 500 m, distance from major roads, and block group population density (R = 0.83; Table 3).
In the final confounder models [see Supplemental Material, Table 1 (http://www.ehponline.org/members/2008/11711/suppl.pdf)], we readjusted the number of degrees of freedom (df) for the smooth function of time trend, because many of the meteorologic variables exhibit seasonal patterns themselves and hence capture part of the observed seasonal trends in the outcome (Touloumi et al. 2004).
We tested the sensitivity of the df of the smooth function of time trend by allowing for different df (i.e. 2, 3, 4, 6 and 8).
