Ipsos Encyclopedia - Purchase Intentions

Definition: Purchase intent is one of the most long-standing and widely used measures in marketing research. Its use spans different types of research (new product testing, product testing, package testing, copy testing, ad touchpoint effectiveness, innovation and brand positioning, and loyalty).

Ipsos Encyclopedia - Purchase Intentions

Purchase intent may be a KPI (e.g., in testing), an input in modelling (e.g. forecasting), or a dependent measure in modelling (ad touchpoint effectiveness, innovation and brand positioning).

The most common wording of the question uses a 5 point scale:

How likely would you to be purchase?

  • Definitely will buy
  • Probably will buy
  • Might or Might Not Buy
  • Probably Will Not Buy
  • Definitely Will Not Buy

There has been R&D in new product research that connects each of these answers to the probability of actual purchase in the next year.  Each 'box' of purchase intent (definitely will, probably will, etc.) is generally assigned a different probability.  A easy rule of thumb to remember is 81%, 27%, 9%, 3%, and 1% (known as the powers of 3).  Other rules exist such as 75% top box and 25% second box and 0% for all remaining boxes.  It is known, though, the actual probability of purchase depends on the category or the category purchase cycle, with the probability lower for products in categories with longer purchase cycles.  In addition, for higher priced items such as those in technology or durables categories, the price of the product is also a factor in determining the weights.

Another version of the scale which has been used by some companies for durable goods is the 11 point Juster Scale.

  • Certain, practically certain (99 in 100)
  • Almost sure (9 in 10)
  • Very probable (8 in 10)
  • Probable (7 in 10)
  • Good possibility (6 in 10)
  • Fairly good possibility (5 in 10)
  • Fair possibility (4 in 10)
  • Some possibility (3 in 10)
  • Slight possibility (2 in 10)
  • Very slight possibility (1 in 10)
  • No chance, almost no chance (1 in 100)

The 11 Juster point scale has been found to offer somewhat better discrimination.  Also, the use of labels and numbers is helpful for respondents who tend to be more text or numbers focused.  However, the use of the 11 point scale is rare because there is so much learning on the 5 point scale and the 5 point scale is simpler.    

Purchase intent is widely accepted because it has face validity (i.e. measures what it intends to measure), it has been proven to be predictive, it is a simple single measure, and it has a behavioural orientation.  A number of companies have formed action standards based solely on purchase intent or based a small set of measures including purchase intent. 

There  are some things that are important to know when using purchase intent.  First, it tends to penalise uniqueness, unless what is being evaluated is well understood (note that breakthrough innovations score poorly on purchase intent).  Second, it can be strongly influenced by the absolute price of what is being evaluated.  Third, it is highly variable from one country to other and the top box and second box can be very high in developing markets.  Fourth, it is quite sensitive to executional elements.  For example, if you show a concept or ad, purchase intent can be sensitive to the quality of the copy, the images used for packaging, people, or scenery, the price (the absolute level, its location in the stimulus and font size), the number of items in a product line, the use of emotional language or humour, etc.     

If these factors are considered appropriately, then purchase intent can be a very useful measure for evaluation or modelling.

Ipsos Point Of View

The use of purchase intent varies by Ipsos specialism.  In Ipsos Connect ,purchase intent is used to derive a  measure of persuasion when comparing a test cell to a control.  In Brand Graph 360, purchase intent is the dependent measure in a model which measures the effectiveness of advertising touchpoints.  In Vantis, purchase intent is one of several KPIs used to evaluate and forecast innovations and to create archetypes.  In the CPG business of InnoQuest, purchase intent is used mainly as a diagnostic only (instead, Relevance, Expensiveness and Differentation are used as KPIs).   

For InnoQuest, purchase intent is fine to use as one of several measures for evaluation as a KPI (Vantis) or as a diagnostic (CPG), however purchase intent should not be the only or primary measure for evaluation (see the paper PI losing its appeal).  

For Connect, purchase intent is a very important measure.  It is a direct measure of persuasion which is a Connect KPI for copy testing.  Connect has another measure of persuasion (pre-post brand switching which is more appropriate for certain situations).

Purchase intent is appropriate as a dependent measure in modelling when the modelling is not taking into account competition such as in modelling of advertising touchpoints. 

However, when we do modelling which takes into account competition then other measures are more appropriate such as a ranking on performance or a preference measure based on a chip game.  This type of measures provides better discrimination than purchase intent. 

Also, purchase intention works better as a measure of evaluation or in modelling if price is an independent variable, since purchase intent naturally incorporates price.      

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