statistically speaking... guardian writer is confused about statistics

This piece by guardian writer Barbara Ellen probably needs to be rechecked by their sub-editors for statistical correctness.

If you really think you're gay, guys, why not act on it?

http://www.theguardian.com/commentisfree/2013/dec/01/women-same-sex-experimenting

The latest National Survey of Sexual Attitudes and Lifestyles revealed many things (from unplanned pregnancies to unreported sexual assaults), but also that there has been a 400% increase in (mainly younger) women, some fully lesbian, declaring same sex sexual experimentation – around 16%. By contrast, the number of men who'd had a same sex experience had only gone up 1% (to 7%) since 1991.

The data that Barbara Ellen is quoting appears to be this:

Percentage of the population who have ever had same-sex experience (people aged 16-44)

Men(1990-1991):6%
Men(2010-2012):7%

Women(1990-1991):4%
Women(2010-2012):16%


So I think there are two problems with the quoted statement above.

1) There has been a 300% increase in women declaring same sex experimentation.

The absolute increase of 4% to 16%, is 12%... and 12% is 300% of the 1991 figure of 4%.

2) Barbara is also comparing the change in the proportion (of women declaring same sex experimentation) as a percentage of the original 1990-91 value (which should be 300%), to the absolute change (of men declaring same sex experimentation), from 6% to 7%, which is 1%.

However these are not equivalent values. The correct comparison figure for men (of percentage change in proportion of population), to the 300% figure would be 16%, i.e.  

The change from 6% to 7% is a 16.66% increase, when looked at as a percentage change in the proportion.

So the correct way of describing that would be:

"also that there has been a 300% proportional increase of (mainly younger) women, some fully lesbian, declaring same sex sexual experimentation – around 16%. By contrast, the proportional change in percentage of men who'd had a same sex experience  was only 16.66% (to 7%) since 1991."

However, it would also be possible to look at both figures as absolute changes, and that would result in the following correct version:

"also that there has been a 12% absolute increase in (mainly younger) women, some fully lesbian, declaring same sex sexual experimentation – to around 16%. By contrast, the number of men who'd had a same sex experience had only gone up 1% (to 7%) since 1991."

I might be wrong about the interpretation, if I am using the wrong source data...