An inexpensive method for making data records of complex behaviors.

Rilling et al. (1969) built a cheap classroom camera rig. They set a time-lapse camera on a shelf and let it run. The film gave a permanent, replayable record of every student move or teacher contact.

No kids were treated. The paper only shows how to build the rig and why it beats pencil notes.

The authors did not run an experiment. They simply said, “Mount a camera and you will never lose data.”

Iwata et al. (1990) later proved you can skip the film. They used 15-second momentary time sampling in real classrooms and got numbers that almost matched continuous footage. Their method is cheaper and faster than developing reels.

Sisson et al. (1993) then warned that momentary time sampling can lie. If the behavior happens in quick bursts, the 15-second glance can miss most of it. The camera record would have caught every burst, so the two papers do not clash—they just show the trade-off you accept when you give up the camera.

Gardenier et al. (2004) added another red flag. They showed that partial-interval recording balloons duration scores for stereotypy. Again, the old camera would have given the true length, but filming is costly, so interval methods stuck around.

Today you can grab a phone, start time-lapse, and have the same permanent record M et al. wanted. Use it when you need to defend your data in an IEP meeting or when interval methods might miss short, scattered responses. For daily progress monitoring, stick with 15-second momentary time sampling and just remember its limits.