In the early 20th century which party you voted for would usually be determined by which party the persons strongly identify with or infact if they have been brought up around strong certain party supporters Eg both mother and father voting Conservative. Also a person's job could sway how they voted it was typical that middle class business owners would typically vote conservative which is why this party was nicknamed the Political party of the rich whereas lower class working families would tend to vote labour as this party's policies were in the interest of working class families and particularly those involved in trade unions.
However, since the turn of the 20th century, this is much less likely to be the case as evidence shows that there is a great decrease in the percentage of people who vote by party identification. It has fallen from 45% in 1964 to 10% in 2010, it is apparent that voting may be becoming an issue of deliberate choice, a rational exercise rather than something decided by your upbringing or you social class group.
A reason to argue for the statement is when we take into account party leadership and how this has affected general elections, past elections have demonstrated that the face of a political party is infact of most importance to us and there is evidence of significant swings towards one party due to party leadership.An example of such an occasion was the 1979 general election. Labour leader Michael Foot was a kind-hearted man, an ex-pilot and had credible policies, yet he cared not for his appearance and was often quite poorly dressed. Margaret Thatcher on the other hand was well-spoken, well-dressed and an looked the part of a prime-minister - and it was her that won the election. This is evidence that voting is infact a rational excersise.