Two suppliers’ set times on the same ward: a fair comparison

Two drums, side by side on the sluice bench, both labelled 25 g per litre, both claiming a set in under a minute. The ward manager had tried both and concluded that the one on the left was noticeably faster. The one on the left had also been the one she tested first, with a sample collected five minutes earlier, while the one on the right got a bottle that had been standing since the early round.

That is not a comparison. That is two experiments with different conditions and a conclusion drawn from the difference in the conditions.

Fix the five variables

Set time is not a single number. It depends on volume, temperature, urine concentration, agitation and dose. Change any one of them and you can move the result by a factor of three without touching the product.

Five variables, ten minutes of preparation, and a result you can defend in a tender meeting.

Define the end point before you start

This is where most trials fall apart. One tester calls it set when the surface looks dry. Another calls it set when the beaker can be inverted. A third calls it set when a scoop stands upright in it. Those three end points can be two minutes apart on the same sample.

Pick one and write it down: the beaker can be turned through 180 degrees for five seconds and nothing moves. That is a set you can carry, which is the only property that matters on a round.

Record two times for each product: time to surface dry, and time to invertible. The second is the one you buy on. The first is the one that makes a carer think the job is done.

Run five, not one

A single pair of tests tells you almost nothing, because the variation within one product is often larger than the difference between products. Run five alternating trials, A then B then A then B, and take the median. Alternating matters: it averages out any drift in the sample, the room temperature and the tester’s technique.

If the medians are within 15 seconds of each other, treat the products as equivalent on speed and compare them on something that actually differs, such as dust, packing format or price per correct dose. Chasing a ten-second difference is not worth a contract change.

A trust we worked with ran this properly and found a 40-second gap between two products that both claimed under a minute. The slower one was cheaper by 18% and the ward’s containers were emptied within an hour anyway, so the gap cost nothing. They bought the slower one, and the savings paid for a year of sachets on the renal unit.

The test that matters more than speed

Gel strength at one hour. Take the invertible beaker, leave it for an hour, then turn it upside down over a sink for thirty seconds. A weak gel will release liquid at the edges or slump. A strong one will sit there.

This is the number that predicts whether a container will still be intact at the end of a shift, and it is the number that suppliers rarely quote because it depends on the urine as much as the polymer.

Run it on the same day, with the same sample, and you have a comparison that will survive scrutiny from a supplier’s technical team, which is exactly the audience that will challenge it.

Write it up in one page. Date, room temperature, sample source, volumes, doses, the end point definition, five results per product, and the medians. One page, signed by the person who ran it. Photograph the beakers at each time point, because the photograph is more persuasive than the table.

Then put the page in the tender file. When a supplier claims a set time that your own data contradicts, you have an answer that is not an opinion.

The solidification guide describes the volumes and doses to hold constant, so the only thing changing between your two tests is the product.

Book the sluice for an hour, borrow a thermometer and a scale, and settle it properly. One hour of testing beats a year of impressions.