Although you can refer to views declared later in the hierarchy, the XML document is still parsed sequentially. The first time that you refer to a particular ID, you have to prefix it with @+id. In actuality, you can prefix every reference to an ID with @+id and everything will work — in fact, this is what happens if you design your interface with the graphical editor. Just to be safe, everything is prefixed with @+id. The + simply tells it to generate an ID in R.java if and only if it has not already been defined. If you try to define it more than once, it just sees that it’s already been defined and continues on normally.
In your XML, you reference imagearrow_id from your percentage_id TextView. However, at this point the imagearrow_id has not yet been defined. For this scenario, you could simply prefix the layout_toLeftOf=@+id/imagearrow_id in your TextView, and then below, when defining your ImageView (imagearrow_id), you would not need the + in the android:id attribute.