What hinders the credibility of television dramas? We all know about the "willing suspension of disbelief" which Coleridge described. I usually start watching every drama with my natural scepticism switched off but, quite often, something in the programme beggars belief.

This is particularly true of period dramas, where anachronisms can undermine authenticity. The most frequent bugbear is anachronistic language or behaviour. Thankfully, the language didn't clash too much in Mansfield Park (ITV1), although there were more of those modern elisions ('I'm', 'let's' and so on) than I remember in Jane Austen's dialogue. But there was anachronistic behaviour - such as the heroine, Fanny Price, continually running downstairs and along corridors. Such indecorous behaviour from a young woman would have been unthinkable in Austen's time - as would Miss Price's untidy hair.

However, Billie Piper was convincing as Fanny Price, capturing the essence of her humble, caring nature. Both she and Blake Ritson (as Edmund) managed to make good people interesting. Yet the compression of the novel into two hours (minus commercial breaks) made the plot feel hurried and insubstantial, and there was insufficient time to establish some of the characters. This was the first of three Austen adaptations commissioned by ITV and it only suffered a little by the stated aim of being "very 21st century". Let's hope the remaining two dramatisations avoid the temptations of handheld cameras and modernised manners.

Mobile (ITV1) is very modern - a three-part drama in which nearly everyone has mobile phones and uses them repeatedly. This upsets someone unknown, who paints the slogan "Mobile phones are the instruments of Beelzebub" wherever he blows up a phonemast or shoots someone talking on a mobile. It's a gritty northern drama set in Liverpool and Manchester and it carries the viewer along with its mysterious plot. Yet it undermines belief with some improbable events - such as the police's failure to arrest the prime suspect much earlier in the first episode.

The producers of The Yellow House (Channel 4) clearly took some care to create a realistic look for this drama set in 1888. Based on Martin Gayford's book of the same name, it described the period when Gauguin and Van Gogh shared a house in Arles. It told how "in the nine weeks they lived together in penniless obscurity, they produced between them over 40 acknowledged masterpieces".

But these words appeared as a caption at the end of the programme, and the drama concentrated less on the two painters creating these masterpieces and more on their repeated squabbles. At least it showed how the two artists - authentically portrayed by John Lynch and John Simm - educated one another, with Gauguin ostensibly trying to teach things to Van Gogh but actually learning a lot from him. And the drama even explained how Van Gogh famously came to cut off (part of) his ear.

Shark (Five) is a new American series which starts from an unlikely premiss and proceeds in equally incredible mode. It stars hatchet-faced James Woods as Sebastian Stark, a defence lawyer who gets rich by getting baddies acquitted. But he is conscience-stricken when a criminal he defended goes on to commit another brutal crime. Stark changes sides and goes to work as a prosecutor for the District Attorney. Naturally he wins his very first case by a dubious coincidence. It's watchable tosh, but tosh nonetheless.

Ten Kids and Counting (Five) may not have been incredible but it was certainly startling. It looked at five families each with ten or more children. One family has 13 kids, with names including Kylie, Tracy, Chantelle, Candice, Shannon and (I think) Porsche Mercedes. Another family, the Wilsons, also have 13 children, but the mother has fertility treatment because she is desperate to have another child.

Why do they do it? Some parents said they just like children; others claimed that it made them feel needed; and a Catholic family cited religious beliefs. Whatever the reason, it makes a rather unsettling change from the average birthrate of 1.6 children per family.