The population is the collection of response variable measurements on all
experimental units in the universe. The collection of observations of IGF-1 receptors on
each gingival tissue sample make up the population. The U-sample is the collection of
experimental units included in the study and the P-sample is the collection of response
variable measurements from the U-sample. In this report the U-Sample is the collection
of gingival tissue samples in this study and the P-Sample is the expression of IGF-1
receptors on the human gingival tissue samples collected.
This is an observational study as it contains only observational factors. The
response variable is ordinal as it can be ranked subjectively (grade I, II, or III). Ordinal
response variables are the only type of response variable which do not have common
distributions to determine mathematically. Hence, they are referred to as distribution
free. The statistical analysis of ordinal response variables has historically not involved
parameters. This has led to the development of a group on analyses generally referred to
as nonparametric because they are not based on population parameters. Thereby
validating the use of analysis for linear trend and proportions.