How can I increase the size of the marker symbol in legend?

Hi, I am having a trouble with chaning the marker size in legned. I plotted some graphs as follows.

    plot(Model.Period,Model.QQ,'o','MarkerEdgeColor','k', 'LineWidth', 2, ...
        'MarkerFaceColor','none','MarkerSize',3);
    ylabel('Q(cms)','FontWeight','bold');
        hold on;
    area(Model.Period,Model.QQ, 'FaceColor',[.6 .9 .8],'EdgeColor','k');
        hold off;
    xlim([min(Model.Period) max(Model.Period)]);
    Graph.leg3 = legend('Q as o-symbol','Q as area plot');
    set(Graph.leg3,'Location','NorthEast', 'FontWeight', 'bold').

I want to increase the size of marker in the legend without changing the marker size in the graphs. Can you help me, please? Thank you.

[Azzi Abdelmalek]

duplicate question at http://www.mathworks.com/matlabcentral/answers/50250-how-can-i-change-the-marker-size-in-legend