網路調查挾其快速、量大、便利、觸角廣泛之優勢，挑戰傳統調查方法的效益，卻因無法克服機率抽樣與回覆率之根本問題，難以撼動傳統調查的價值。本文以檢討網路調查的限制為出發點，從兩項抽樣設計來比較、探索網路人口的樣本特性。第一項抽樣針對網頁調查的填答者加以追蹤，得到的「網調追蹤樣本」（n=76）是由多次回覆網路調查者所組成；第二項則透過個人網絡進行排他式的滾雪球抽樣，所得「個人網絡樣本」（n=107）則由近似一般網路使用者組成。兩群樣本的網路使用者共提供4492筆過去一個月內和電子郵件聯繫對象之間的關係，以及4674筆過去兩週內收到的一對一信件記錄、3504筆發出的一對一信件記錄。文中分別在個人、聯繫關係、信件接觸三層次上分析兩群樣本的差別。兩群樣本除了在人口特徵及網上行為有些微差異外，最主要的差別在於回覆網路調查者對網路上的聯繫有著特殊立場與傾向；線上聯繫在生活中有其重要性，可是對進入自己網路世界的訊息，可以稍縱即逝，不值得久留。網路調查樣本在對網路使用的態度甚至價值觀上，的確有其特色；依此推論，一般網路調查所反映出來的網路人口，很可能是對網路媒介有特殊評價的一群。對這點偏頗和限制，從事網路調查者必須牢記在心。

　　Online surveys challenge traditional social surveys with several advantages. Due to non-probability sampling and low response rates, however, most online surveys face fundamental flaws. This paper reviews these flaws and limits by exploring key characteristics of online samples. The study employs two sampling designs to collect data. One design follows those who responded to earlier web survey, while the other uses exclusive snowball sampling by personal networks. The resulting “online survey follow-up” sample (n=76) and “personal networks” sample (m=107) contribute to a total of 4492 relationships with alters in the email communication during the past 30 days, and 4674 incoming as well as 3504 outgoing one-on-one personal emails during the past 14 days. These three sets of data are joined and analyzed respectively at the individual, relationship, and contact levels. Major findings suggest that the active respondents in online surveys show distinctive attitudes and values toward the use of online communication. To them the messages exchanged online are important. But the transactions are so transient and fleeting that most messages are not worth keeping. The differences between the two samples are significant and unique in that no other sample characteristics show similar patterns, which further indicates the idiosyncratic tendency among the samples collected by online surveys.