(Reuters) - Twitter Inc said in a blog it would provide its advertisers with custom data-driven reports to help them gauge the impact of their ad campaigns on their profits.

The effectiveness of an ad campaign will be measured by dividing an advertiser's target audience into two groups - one that sees the ads and another that does not - and comparing conversions across the two test groups.

Twitter's ad revenue per monthly average user has been declining and to stem this it has launched new advertising products, notably its app install ads.