It is imperative that the time interval (or period of time) be shown in the heading of each income statement, statement of stockholders' equity, and statement of cash flows. Labeling one of these financial statements with "December 31" is not good enough–the reader needs to know if the statement covers the one week ended December 31, 2015 the month ended December 31, 2015 the three months ended December 31, 2015 or the year ended December 31, 2015.