For the first 11 years of her life, Avantikapa, now 12, grew up without a toilet in her house in West Bengal's East Midnapur district. As she approached adolescence and felt increasingly uncomfortable with the multiple risks of open defecation and the sheer embarrassment of it, Avantikapa spoke to her parents and got them to build a toilet at home. "I don't have to worry about dogs, I don't have to go under the cover of night," she says happily.

In East Sikkim, a co-education school has seen attendance of girl students improve after toilets were built inside the school. "Earlier, they would go in the bushes. Many students fell ill with diarrhoea, and it became harder to find places to defecate. Now many girls who dropped out of school have come back for further studies," says school principal Aarti Gautum.

These are two heartening stories of the success of Prime Minister Narendra Modi's Swachh Bharat Mission. But anecdotal evidence is an imperfect method of impact assessment. For decades, public discourse about the impact of sanitation programmes has been informed by anecdotal evidence from the other end of the spectrum: Toilets are constructed only in government files and, even if made, are never used for practical or cultural reasons. Whether positive or negative, this gives, at best, a skewed understanding of the impact of social sector schemes. That is why three years into the mission, the Quality Council of India (QCI) launched a massive survey of rural sanitation to gather empirical evidence and measure service levels against promises.

QCI is a national accreditation body that has been involved in most of the marquee Swachh Bharat schemes to evaluate sanitation performance through an internationally bench-marked evaluation matrix. It's an article of faith in the most reputed management courses that what gets measured gets improved. With a continent-size population of 1.3 billion plus, it is implicit that any outsize scale project like Swachh Bharat must constantly measure the right metrics.

The survey, Swachh Survekshan Gramin 2017, covered 140,000 households across 700 districts. QCI surveyors personally visited the households to physically verify if they had a toilet, and if they had one, were the toilets were being used. Every enumerated household was geo-tagged to lend the survey authenticity. The survey, conducted over six months ending in August 2017, threw up stunning results.

In their criticism of the Swachh Bharat Mission, many have cited anecdotal evidence about toilets being used to store grains, but the QCI survey gathered empirical evidence of a dramatic improvement in both coverage and usage of toilets. Three years after the launch of the mission, a behavioural change is discernible, especially in rural India.

Let the figures do the talking: As per Census 2011, more than five in 10 households did not have a toilet or individual household latrine (IHHL) in technical lingo. Further broken down, this translated to nearly seven in 10 rural homes not having a toilet and almost two in 10 urban homes where family members had to defecate in the open. Against that, the survey found, only less than three in 10 households (26.75 per cent) are without a toilet in the country (against 50 per cent as per the 2011 census). The improvement is dramatic in rural India where the number of households without toilets has come down to 32.5 per cent (from 69 per cent). That is, toilet coverage has more than doubled in rural India in these three years. For urban areas that number is 14.5 per cent (down from 18 per cent).

Now on to toilet usage. The survey found that more than nine in 10 (91.29 per cent) rural households having access to a toilet are actually using it. The results are similar for urban areas. Of 73 cities that participated in Swachh Survekshan 2016, 54 cities have improved their score in overall municipal solid waste management in 2017. Here again, there is anecdotal evidence that open defecation persists in cities declared ODF but these are isolated cases. Even if we are not yet at 100 per cent, isn't 90 per cent plus a remarkable number, considering the daunting scale of the mission?

The Swachh Bharat urban and rural projects have set-off healthy competition among cities and districts. Self-help groups, NGOs and popular icons have pitched in and the results are showing in the form of a record number of sustainable toilets, open defecation-free towns, schools with gender specific toilets and decrease in water borne diseases in ODF villages and towns.

The public health benefits of ODF spaces far outweigh any criticism of non-compliance. Swachh Bharat is getting a state push but at its best, it's a social project where we are all conscience-keepers. If funding and resources for local bodies are one end of the spectrum, equally crucial are social factors such as caste, gender and poverty.

The three-pronged job of measuring, ranking and naming-shaming is working and we must leverage this approach across domains. Railways and Ports Authority have already begun implementing similar projects. So far, the QCI has measured toilets built, usage, ODF and structural issues such as sewage systems and solid waste removal systems. As these achieve usage at scale, we should also measure behaviour changes. Pouring concrete alone won't solve the problems of public hygiene. The combination of a people's movement and the force multipliers of infrastructure readiness and impact measurement can deliver results very quickly.

But just as real as the figure the survey has thrown up is the fact that hundreds of Indians die from preventable conditions each year even now, especially in places which have maximum incidence of open defecation. Faeces in groundwater spread encephalitis, an annual post-monsoon scourge, diarrhoea stunts children and adults and underweight mothers produce babies prone to sickness. The cycle is lethal.

The costs of public health crises are far greater than the price of fixing it. That is why Swachh Bharat must power on, its efficacy sharpened by regular impact assessment studies and the learning they provide.