People were once concerned that being exposed to more than one language would be confusing and cause bilinguals to lag behind their monolingual peers in language development, but multiple researchers have refuted this claim. Bilinguals appear to acquire the same milestones—including when they say their first word, when they say their first telegraphic phrase, and when they obtain a vocabulary of fifty words—within the "normal range of variation" of monolingual development in each language. This is an analysis of overall vocabulary in bilinguals, as this is the more accurate and appropriate measure of language development in bilinguals. Analyzing only one of a bilingual individual's languages would seriously underestimate their true vocabulary knowledge. Note that any vocabulary deficits in one language are likely filled by knowledge in the other language, suggesting a likelihood that bilinguals know more vocabulary words than monolinguals in general. To this effect, researchers emphasize the importance of assessing overall vocabulary in bilinguals because assessing only one is an underestimation of their true knowledge, and when assessed in overall vocabulary bilingual children were no different from monolingual children in terms of language development.