How often you should advertise depends upon several key points. How thin is your market? How considered is the purchase (recency)? How much competition do you have? Other variables include:
Is it a new campaign? To establish awareness of a new campaign, a higher level of frequency is required. An ongoing campaign can use a lower frequency level since it is a “reminder” situation.
Is the store or service dominant in its category? A brand that is dominant in its category might require less frequency due to existing higher consumer acceptance levels and a generally higher level of awareness. Consequently, a minor brand will require a higher level of frequency to establish its market position.
Brand loyalty. The higher the brand loyalty in purchasing the product or service on the part of the public, the lower the frequency requirements.
Competitive stance in the marketplace. If the determination is made to meet or beat the competition in the market, then higher frequency is probably needed.
Remember that the higher the level of competitive advertising in the market, the higher the frequency required to maintain a share of the voice.