How sampling works
Sampling in Analytics is the practice of selecting a subset of data
from your traffic and reporting on the trends available in that sample
set. Sampling is widely used in statistical analysis because analyzing
a subset of data gives similar results to analyzing all of the data.
In addition, sampling speeds up processing for reports when the volume
of data is so large as to slow down report queries.
When sampling is applied
Specifically, Analytics inspects the number of sessions for the
specified date range at the property level. If the number of sessions
in the property over the given date range exceeds 250k sessions (25M
for Premium)1, Analytics will employ a sampling algorithm which uses a
sample set proportional to the distribution of sessions by day for the
selected date range. Thus, the session sampling rate varies for every
query depending on the number of sessions included in the selected
date range for the given property.
You cant prevent sampling.
HIGHER_PRECISION — Returns a more accurate response using a large
sample size, but this may result in the response being slower.
Check your response it will tell you if the data is sampled
