English grammar | confusing nouns Changes to the exam format could have a serious influence on candidates. [incorrect] Changes to the exam format could have a serious effect on candidates. [correct] It is difficult to assess the impact of the disaster on tourism. It is difficult to assess the extent of the disaster on tourism. An influence is something which causes people to think or behave in a different way: We need to learn more about the influence of violent computer games on young people . Our experiences have a huge influence on our personality . An effect is what happens to someone or something as a result of something else: Research has shown the harmful effects of stress on mothers and unborn babies . The new resort has had a beneficial effect on local businesses . [not effect to ] * Remember, effect is a noun. The verb form is affect: Homes on the west coast were seriously affected by the hurricane . An impact is a powerful effect of something,