Which of the following is often said not to be a purely random sampling method?

Systematic sampling is often said not to be purely random because only the first unit is chosen at random.

Stratified random sampling uses genuine randomization within each stratum.

Simple random sampling is the pure form where every unit has an equal, independent chance.

Lottery-based random sampling is a direct, fully random drawing of units.

After the random start the remaining units follow a fixed interval, removing independence.

This makes systematic sampling technically quasi-random rather than fully random.