If the data set is a statistical population (i.e., consists of every possible observation and not just a subset of them), then the mean of that population is called the population mean and denoted by the Greek letter .
ɪf ðə dˈeɪɾə sˈɛt ɪz ɐ stɐtˈɪstɪkəl pˌɑːpjʊlˈeɪʃən ˈaɪ.ˈiː., kənsˈɪsts ʌv ˈɛvɹi pˈɑːsᵻbəl ɑːbzɚvˈeɪʃən ænd nˌɑːt dʒˈʌst ɐ sˈʌbsɛt ʌv ðˌɛm, ðˈɛn ðə mˈiːn ʌv ðæt pˌɑːpjʊlˈeɪʃən ɪz kˈɔːld ðə pˌɑːpjʊlˈeɪʃən mˈiːn ænd dᵻnˈoʊɾᵻd baɪ ðə ɡɹˈiːk lˈɛɾɚ .