A practical example of a one-group posttest only design is measuring elementary school students' attitudes toward illegal drugs immediately after they complete an anti-drug education program, without any prior measurement or control group. Another common example involves media reports, such as an advertiser claiming that $80\%$ of women noticed brighter skin after using a specific cleanser for a month. In both cases, the lack of a comparison group makes it impossible to draw meaningful conclusions about the actual effectiveness of the treatment.