age_list_gen function

Age Trend Estimates Generation

A GAMLSS model using a Normal distribution was fitted separately to rois of interest, to establish normative reference ranges for the volume of a specific ROI as a function of age, adjusting for sex and intracranial volume.

age_list_gen(
  sub_df,
  lq = 0.25,
  hq = 0.75,
  mu = "smooth",
  sigma = "smooth",
  nu = "default",
  tau = "default"
)

Arguments

• sub_df: A four-column dataset that contains age, sex, intracranial volume (ICV) and roi volume related information. The columns for age, sex, and ICV must be strictly named "age", "sex", and "icv".
• lq: The lower bound quantile. eg: 0.25, 0.05
• hq: The upper bound quantile. eg: 0.75, 0.95
• mu: An indicator of whether to smooth age variable, include it as a linear term or only include the intercept in the mu formula. "smooth": y ~ pb(age), "linear": y ~ age, "default": y ~ 1.
• sigma: An indicator of whether to smooth age variable, include it as a linear term or only include the intercept in the sigma formula. "smooth": ~ pb(age), "linear": ~ age, "default": ~ 1.
• nu: An indicator of whether to smooth age variable, include it as a linear term or only include the intercept in the nu formula. "smooth": ~ pb(age), "linear": ~ age, "default": ~ 1.
• tau: An indicator of whether to smooth age variable, include it as a linear term or only include the intercept in the tau formula. "smooth": ~ pb(age), "linear": ~ age, "default": ~ 1.

Returns

age_list_gen returns a list containing the following components: - true_df: a dataframe contains the true age and ROI volume information

• predicted_df_sex: a dataframe contains the estimated age trend adjusting sex and icv

• model: the fitted GAMLSS model

Examples

sub_df <- age_df[,c("Volume_1", "age", "sex", "ICV_baseline")] |> na.omit()
colnames(sub_df) <- c("Volume_1", "age", "sex", "icv")
age_list_gen(sub_df = sub_df)