In Soviet times, the usage of Ukrainian gradually decreased, particularly during those times when the Russification policies intensified (i.e. in the 1930s and during the late 1970s to early 1980s), and so a sizable portion of ethnic Ukrainians possess a better knowledge of formal Russian than of formal Ukrainian. Since 1991, however, Ukrainian has been the sole official language. After this change, it was realised that much of the population of Ukraine was actually unable to speak Ukrainian fluently. This was highly apparent in the case of many Ukrainian officials (including the President of Ukraine), who were observed to make code-mixing mistakes in their speech.