Answer
$The\:sample\:must\:be\:random,\:meaning\:every\:member\:of$
$\:the\:population\:should\:have\:an\:equal\:chance\:of\:being\:selected.\:$
$This\:ensures\:the\:sample\:is\:unbiased.$
Work Step by Step
$The\:sample\:is\:a\:subgroup\:of\:the\:population.\:The\:sample\:$
$must\:be\:random.\:For\:a\:sample\:to\:be\:a\:random\:sample,\:$
$every\:member\:of\:the\:population\:must\:have\:an\:equal\:chance\:$
$of\:being\:selected.\\When\:a\:sample\:is\:chosen\:at\:random\:from\:$
$a\:population,\:it\:is\:said\:to\:be\:an\:unbiased\:sample.$
