Learn Swedish: Vi behöver dessa siffror för att analysera ökningen. - We need these figures in order to analyze the increase.

The word dessa means "these" and is a formal demonstrative. A strict rule in Swedish is that denna, detta, and dessa must be followed by a noun in its indefinite form. Since the base word is siffra, its indefinite plural is siffror.

If dessa siffror is formal, how would I say this in everyday speech?

In everyday spoken Swedish, you would usually use de här for "these". But remember that de här requires the definite form of the noun. So you would say de här siffrorna instead of dessa siffror.

Why do we use för att before analysera instead of just att?

We use för att when we want to express purpose, meaning "in order to". Whenever you can swap "to" with "in order to" in English, you should use för att before the infinitive verb in Swedish.

What is the base form of ökningen?

The base form is ökning (increase). Nouns ending in -ing in Swedish are almost always en-words. To make it definite ("the increase"), you simply add -en to the end, giving you ökningen.