Ads in some ad groups rarely showing

My adword account is broken into 5 ad groups: 1 for each of 4 key products and an overall ad group.
90% of the impressions and 100% of the clicks go to 2 of the ad groups.

Some of the keywords used in the low-performing ad groups have good search volume. The Google Keyword tool estimates global monthly searches for 1 keyword at 5400, local monthly searches at 4400 per month.
My bids are high enough to display most ads on page 1, yet they get less than 200 impressions per month. Could this be an Adwords setting that is allowing these ads to only rarely show?

 

I've had this exact same issue and looking at the other threads in this forum leads me to believe that my issue at least is Quality Score. Some of my keywords do not have good Click Through Rates and hence have a low quality score. What I see is exactly what's happening to you: words just not getting the impressions you'd expect.

Not sure if cross linking to threads is deemed appropriate here, but take a look as some recent threads on quality Scores etc.

 

Don't think this purely quality score issue...of 20 keywords in this ad group, none have a score below 4. For example, one word has a Qscore of 7...Traffic Estimator says I should expect 880 monthly searches but have had only 22 impressions. 6 other keywords have a 7 Qscore but show a status of "low search volume". I expect these six to provide no impressions, but shouldn't I get something from the others?

PS: Under Advanced Settings, I do have the Ad Rotation setting set to "Show Ads more Evenly" to prevent Google from only showing the better-performing ads.

 

Has to be said, I'm probably too focused on my QS issues and see the same problem everywhere. I'd be interested in the "answer" myself, since anything which can improve impressions would be worthwhile.

A hint I saw elsewhere was to use Google's adpreview tool http://www.google.com/adpreview (my link probably won't show, so you'll need to google it...). This lets you see the ad in situ without incurring impressions and hence lowering your CTR just because you're testing.

 

If you don't get the expected impressions, your daily budget may be too low to get 100% share of the impressions.

 

I'm not spending anywhere near my daily budget every day. And even if I were, why would only 2 ad groups get all the impressions?

 

Me neither. There must be something else going on.