This review summarizes all of 196 web-based studies that were conducted in a nonprofit online panel spanning an interval of 12.5 years. Thirty study characteristics were examined as to how they influence panelists' starting rate and completion rate. These study characteristics pertain to temporal features of the study, attributes of participants invited to the study, panel status at the time the study was conducted and rewards offered for study participation. A higher share of invited panelists called up the first page of a study (a) the fewer panelists that were in the panel in the year of study, (b) the more the panel had grown in the year of study, (c) in the winter, (d) the fewer panelists that were invited to the given study, (e) if the study was an in-house study, (f) if a reminder was sent, (g) if panelists who were invited to the study took part in a previous study, (h) if the length of the study was announced in the study request, (i) the shorter the study and (j) if a per-capita reward was offered. A higher share of responding panelists stayed until the final page of a study (a) in seasons other than winter, (b) the shorter the study and (c) if a per-capita reward was offered. Based on these findings, recommendations are made about how to best conduct online panel studies with a view on the starting rate and the completion rate.