In the Tooltip documentations it says "Tooltip[expr] is equivalent to Tooltip[expr,expr]." but somehow this is not always the case because this works perfectly:
dataMean = {32.4, 32.6, 39.3, 40.1, 45.2, 48.2, 48.8, 51.4, 52.5, 52.9};
dataMedian = {25.0, 27.0, 37.5, 38.0, 45.0, 52.0, 54.0, 59.0, 63.0, 59.0};
dataStDev = {25.1, 23.3, 26.2, 27.6, 26.8, 27.5, 28.3, 26.5, 27.5, 25.9};
ListLinePlot[
Tooltip[{dataMean, dataMedian, dataStDev},
{dataMean, dataMedian, dataStDev}],
InterpolationOrder -> 3 (*Always an ERROR message with 2 or 3,etc.*),
PlotMarkers -> Automatic, PlotRange -> {{1, 10}, {10, 70}}]