C# WPF XAML convert string to boolean

Question

i have a question. How can i convert a variable binding of type string in a variable bool from visibility binding? In my code i have ListBox Visibility="{Binding MultipleQuestion} but i want to bind with value true/false. How can i do that? XAML:

<ListBox Visibility="{Binding MultipleQuestion}" HorizontalAlignment="Left" Height="313" Margin="57,29,0,0" VerticalAlignment="Top" Width="681" SelectionMode="Single"  IsSynchronizedWithCurrentItem="True">

                        <TextBlock Text="{Binding QuestionName}" Margin="25" FontSize="15"/>
                        <ItemsControl ItemsSource="{Binding ItemsControlGet}">
                                <ItemsControl.ItemTemplate>
                                        <DataTemplate>
                                                <StackPanel>

                                                        <CheckBox IsChecked="{Binding CheckItem}" Margin="10" Content="{Binding LoadRadioContent}"/>
                                                </StackPanel>
                                        </DataTemplate>
                                </ItemsControl.ItemTemplate>
                        </ItemsControl>
                </ListBox>

C# code:

public string _MultipleQuestion = "Hidden";
            public string MultipleQuestion
            {
                    get
                    {
                            return _MultipleQuestion;
                    }
                    set
                    {
                            _MultipleQuestion = value;
                    }
            }