摘要：They got 27 per cent of the vote as against 32 per cent at the last election. （他们获得了27%的选票，而上次选举为32%。）[牛津高级学者辞典]

as against相当于汉语“而”，用A事件衬托对比B事件，如

【例句1】They got 27 per cent of the vote as against 32 per cent at the last election. （他们获得了27%的选票，而上次选举为32%。）[牛津高级学者辞典]

【例句2】Profits this year are $2.5 million as against $4 million last year. （今年的利润为250万美元，而去年为400万美元。）[朗文当代英语词典]

【例句3】The study found that the average length of US TV breaks was 141 seconds as against 236 seconds in Britain. （研究发现，美国电视休息时间的平均长度为141秒，而英国为236秒。）[柯林斯高级学者辞典]

【例句4】He earns $80,000 a year, as against my $40,000.（他一年挣8万美元，而我一年挣4万美元。） [剑桥高级学者辞典]

这里的as应该算是修饰介词短语的副词，含义大体为“如此地”；against有“相对抗”之义。

来源：生物小黑板