How a 0–100 index tracks digital’s hold on buying journeys
A SPJIMR student project measures digital influence on real purchase journeys—and finds AI can overstate the role of online platforms.
Marketers have spent decades using tidy academic models to map how people decide. But the purchase journey has changed, and a new SPJIMR student project is trying to put a number on exactly how much.
The birth of a Digital Influence Index
Seventeen student groups at SPJIMR interviewed around 35 consumers each across four age cohorts—16–25, 26–35, 35–49 and 50+—covering categories such as smartphones, apparel, automobiles, personal care, grocery, investments and entertainment. Their goal: build a Digital Influence Index, or DII, that scores how much of a purchase journey is powered by digital platforms.
On the scale, 100 means the journey is entirely digital, and 0 means digital plays no role. The article is quick to note that no real product sits at either extreme. The useful question is how high or low each cohort and category scores.
The AI answer looked confident—and wrong
The professor first asked GenAI platforms how digital shapes buying. The responses were surprising and skewed digital. The explanation is a data blind spot: consumers rarely post their offline behaviour on social feeds. AI can read reviews, posts and search patterns, but not the showroom visits, family conversations or offline comparisons that never get published.
That matters because marketers who treat AI output as primary research risk overestimating digital influence and underfunding the offline touchpoints that still close sales.
Early findings worth watching
Some results were predictable. Car buying, for instance, retains a significant offline component: showrooms, test drives and family discussions still shape the decision. More surprising was grocery, where some segments now buy in a highly digital-driven way.
The project also revives two useful shopper labels:
- Webroomers research online but buy offline.
- Showroomers browse offline but complete the purchase online.
Consumers also use digital platforms to simplify choices. More options create more decision time, so in commoditised categories people lean on simple set processes, while high-involvement purchases keep a stronger human and physical loop.
What brand managers should do
The DII series will run weekly across six articles, so the full category and cohort scores are still to come. But the first lesson is already useful: digital influence is not a single number. It shifts by age, product and journey stage.
Before reallocating budgets, run a similar audit on your own buyers. Pick one product and one age cohort, interview real customers, and score each stage from fully offline to fully digital. Then match your channel spend to where influence actually happens.
Source: ETBrandEquity.com
