CROSS-REFERENCE TO RELATED APPLICATION [0001] Korean Patent Application No. 10-2015-0152524, filed on October 30, 2015, in the Korean Intellectual Property Office, and entitled: “Composite Positive Active Material, Method of Preparing the Same, and Lithium Secondary Battery Including Positive Electrode Including the Same,” is incorporated by reference herein in its entirety. BACKGROUND 1. Field [0002] Embodiments relate to composite positive active materials, methods of preparing the same, and lithium secondary batteries including positive electrodes including the same. 2. Description of the Related Art [0003] Lithium cobalt oxides are widely used as positive active materials of lithium secondary batteries. Nickel-based lithium composite oxides are less expensive in terms of preparation costs and may have superior properties as compared to lithium cobalt oxides. SUMMARY [0004] Embodiments are directed to a composite positive active material comprising a lithium nickel cobalt aluminum composite oxide. A full width at half maximum (FWHM) of a peak of a (104) plane of the lithium nickel cobalt aluminum composite oxide is 0.15 or less and an FWHM of a peak of a (018) plane of the lithium nickel cobalt aluminum composite oxide is 0.15 or less, the peaks being obtained by X-ray diffraction analysis using a CuKα X-ray. 3 An amount of aluminum in the composite positive active material may be in a range of about 5 mol% to about 10 mol% with respect to a total amount of cobalt, nickel and aluminum. [0005] . [0006] A cation mixing ratio in a lithium layer of the composite positive active material may be 5.0% or less based on a total amount of lithium sites. [0007] The composite positive active material may have an average crystal size of 800 nm or less. [0008] The composite positive active material may be a compound represented by Formula 1 below: [Formula 1] LiNiaCobAlcO2, wherein in Formula 1, 0.7≤a<1.0, 0