In addition to this, there are other circumstances which effect; many groups can maintain high earnings and limit supply as they have control over the supply of labour – this is seen notably in professional bodies. Whilst other groups have differing 'degrees of unionisation' and 'industrial power'; for example Gosling found that wage inequality increased as trade union influence weakened .
Furthermore, a study by Johnson and Reed shows that income level and ‘unemployment experiences' of fathers are related to subsequent experiences of their sons. Their case study showed that the sons of fathers, who represented the bottom 20% of earners were over three times more probable to stay in the same income bracket. This is aligned to the generalisation that the number of single parent families is increasing, whom usually undertake part time/unskilled occupations – which has widened the income distribution gap. Incidentally, Gosling also did a study on sex gender and found that women earn only 61% of men’s wages ; it appears that women’s relative income differ to men within