If a researcher wants to select a sample from a population such that each member in the population of interest has an equal chance of being selected in the sample, the researcher is following

Random sampling gives every member of the population an equal chance of selection.

This known equal probability is what makes the sample unbiased and representative.

Quota sampling fills category quotas by non-random selection.

Convenience sampling picks whoever is easily reachable.

Purposive sampling selects units by the researcher's judgement.

Only probability designs like random sampling permit valid statistical inference.